Send notification emails to the "project", and put people in Cc

This fixes email threading in Mail.app, that doesn't like when a thread
doesn't have stable recipients.

For instance, here is a possible sender-recipient combinations before:

From: A
To: Me
New issue

From: B
To: Me
Reply on new issue

From: A
To: Me
Another reply

Mail.app doesn't see B as a participant to the original email thread,
and decides to break the thread: it will group all messages from A
together, and separately all messages from B.

This commit makes the thread look like this:

From: A
To: gitlab/project
Cc: Me
New issue

From: B
To: gitlab/project
Cc: Me
Reply on new issue

From: A
To: gitlab/project
Cc: Me
Another reply

Mail.app sees a common recipient, and group the thread correctly.

6 files changed, 30 insertions, 16 deletions

diff --git a/app/mailers/emails/groups.rb b/app/mailers/emails/groups.rb
index 1654fc55bca..39527b00e9f 100644
--- a/app/mailers/emails/groups.rb
+++ b/app/mailers/emails/groups.rb
@@ -4,7 +4,7 @@ module Emails
       @membership = UsersGroup.find(user_group_id)
       @group = @membership.group
       @target_url = group_url(@group)
-      mail(to: @membership.user.email,
+      mail(cc: @membership.user.email,
            subject: subject("Access to group was granted"))
     end
   end
diff --git a/app/mailers/emails/issues.rb b/app/mailers/emails/issues.rb
index a096df9dc0d..50676ac10cb 100644
--- a/app/mailers/emails/issues.rb
+++ b/app/mailers/emails/issues.rb
@@ -6,7 +6,7 @@ module Emails
       @target_url = project_issue_url(@project, @issue)
       set_message_id("issue_#{issue_id}")
       mail(from: sender(@issue.author_id),
-           to: recipient(recipient_id),
+           cc: recipient(recipient_id),
            subject: subject("#{@issue.title} (##{@issue.iid})"))
     end
 
@@ -17,7 +17,7 @@ module Emails
       @target_url = project_issue_url(@project, @issue)
       set_reference("issue_#{issue_id}")
       mail(from: sender(updated_by_user_id),
-           to: recipient(recipient_id),
+           cc: recipient(recipient_id),
            subject: subject("#{@issue.title} (##{@issue.iid})"))
     end
 
@@ -28,7 +28,7 @@ module Emails
       @target_url = project_issue_url(@project, @issue)
       set_reference("issue_#{issue_id}")
       mail(from: sender(updated_by_user_id),
-           to: recipient(recipient_id),
+           cc: recipient(recipient_id),
            subject: subject("#{@issue.title} (##{@issue.iid})"))
     end
 
@@ -40,7 +40,7 @@ module Emails
       @target_url = project_issue_url(@project, @issue)
       set_reference("issue_#{issue_id}")
       mail(from: sender(updated_by_user_id),
-           to: recipient(recipient_id),
+           cc: recipient(recipient_id),
            subject: subject("#{@issue.title} (##{@issue.iid})"))
     end
   end
diff --git a/app/mailers/emails/merge_requests.rb b/app/mailers/emails/merge_requests.rb
index ea5671c4502..6b46cc90e08 100644
--- a/app/mailers/emails/merge_requests.rb
+++ b/app/mailers/emails/merge_requests.rb
@@ -6,7 +6,7 @@ module Emails
       @target_url = project_merge_request_url(@project, @merge_request)
       set_message_id("merge_request_#{merge_request_id}")
       mail(from: sender(@merge_request.author_id),
-           to: recipient(recipient_id),
+           cc: recipient(recipient_id),
            subject: subject("#{@merge_request.title} (##{@merge_request.iid})"))
     end
 
@@ -17,7 +17,7 @@ module Emails
       @target_url = project_merge_request_url(@project, @merge_request)
       set_reference("merge_request_#{merge_request_id}")
       mail(from: sender(updated_by_user_id),
-           to: recipient(recipient_id),
+           cc: recipient(recipient_id),
            subject: subject("#{@merge_request.title} (##{@merge_request.iid})"))
     end
 
@@ -28,7 +28,7 @@ module Emails
       @target_url = project_merge_request_url(@project, @merge_request)
       set_reference("merge_request_#{merge_request_id}")
       mail(from: sender(updated_by_user_id),
-           to: recipient(recipient_id),
+           cc: recipient(recipient_id),
            subject: subject("#{@merge_request.title} (##{@merge_request.iid})"))
     end
 
@@ -38,7 +38,7 @@ module Emails
       @target_url = project_merge_request_url(@project, @merge_request)
       set_reference("merge_request_#{merge_request_id}")
       mail(from: sender(updated_by_user_id),
-           to: recipient(recipient_id),
+           cc: recipient(recipient_id),
            subject: subject("#{@merge_request.title} (##{@merge_request.iid})"))
     end
   end
diff --git a/app/mailers/emails/notes.rb b/app/mailers/emails/notes.rb
index 8d1f17b0f81..d6ab63fe68c 100644
--- a/app/mailers/emails/notes.rb
+++ b/app/mailers/emails/notes.rb
@@ -6,7 +6,7 @@ module Emails
       @project = @note.project
       @target_url = project_commit_url(@project, @commit, anchor: "note_#{@note.id}")
       mail(from: sender(@note.author_id),
-           to: recipient(recipient_id),
+           cc: recipient(recipient_id),
            subject: subject("#{@commit.title} (#{@commit.short_id})"))
     end
 
@@ -17,7 +17,7 @@ module Emails
       @target_url = project_issue_url(@project, @issue, anchor: "note_#{@note.id}")
       set_reference("issue_#{@issue.id}")
       mail(from: sender(@note.author_id),
-           to: recipient(recipient_id),
+           cc: recipient(recipient_id),
            subject: subject("#{@issue.title} (##{@issue.iid})"))
     end
 
@@ -28,7 +28,7 @@ module Emails
       @target_url = project_merge_request_url(@project, @merge_request, anchor: "note_#{@note.id}")
       set_reference("merge_request_#{@merge_request.id}")
       mail(from: sender(@note.author_id),
-           to: recipient(recipient_id),
+           cc: recipient(recipient_id),
            subject: subject("#{@merge_request.title} (##{@merge_request.iid})"))
     end
 
@@ -37,7 +37,7 @@ module Emails
       @project = @note.project
       @target_url = project_wall_url(@note.project, anchor: "note_#{@note.id}")
       mail(from: sender(@note.author_id),
-           to: recipient(recipient_id),
+           cc: recipient(recipient_id),
            subject: subject("Note on wall"))
     end
   end
diff --git a/app/mailers/emails/projects.rb b/app/mailers/emails/projects.rb
index 9f99c11ea30..6017d9192ec 100644
--- a/app/mailers/emails/projects.rb
+++ b/app/mailers/emails/projects.rb
@@ -4,7 +4,7 @@ module Emails
       @users_project = UsersProject.find user_project_id
       @project = @users_project.project
       @target_url = project_url(@project)
-      mail(to: @users_project.user.email,
+      mail(cc: @users_project.user.email,
            subject: subject("Access to project was granted"))
     end
 
@@ -12,7 +12,7 @@ module Emails
       @user = User.find user_id
       @project = Project.find project_id
       @target_url = project_url(@project)
-      mail(to: @user.email,
+      mail(cc: @user.email,
            subject: subject("Project was moved"))
     end
 
@@ -30,7 +30,7 @@ module Emails
       end
 
       mail(from: sender(author_id),
-           to: recipient,
+           cc: recipient,
            subject: subject("New push to repository"))
     end
   end
diff --git a/app/mailers/notify.rb b/app/mailers/notify.rb
index 84a0da0129d..8eea8cf25e0 100644
--- a/app/mailers/notify.rb
+++ b/app/mailers/notify.rb
@@ -1,4 +1,6 @@
 class Notify < ActionMailer::Base
+  include ActionDispatch::Routing::PolymorphicRoutes
+
   include Emails::Issues
   include Emails::MergeRequests
   include Emails::Notes
@@ -16,6 +18,7 @@ class Notify < ActionMailer::Base
   default_url_options[:script_name] = Gitlab.config.gitlab.relative_url_root
 
   default from: Proc.new { default_sender_address.format }
+  default to:   Proc.new { project_sender_address.format }
   default reply_to: "noreply@#{Gitlab.config.gitlab.host}"
 
   # Just send email with 2 seconds delay
@@ -32,6 +35,17 @@ class Notify < ActionMailer::Base
     address
   end
 
+  # The default email address to send emails to. Includes the project name if possible.
+  def project_sender_address
+    if @project
+      address = default_sender_address
+      address.display_name = @project.name_with_namespace
+      address
+    else
+      default_sender_address
+    end
+  end
+
   # Return an email address that displays the name of the sender.
   # Only the displayed name changes; the actual email address is always the same.
   def sender(sender_id)