Groups and collection: initial integration

Since we are ditching layers from Blender (2.8) we need a replacement to
control groups visibility. This commit introduces collections as the building
blocks for groups, allowing users to control visibility as well as overrides
for groups.

Features
========

* Groups now have collections
    This way you can change the visibility of a collection inside a group, and add
    overrides which are part of the group and are prioritized over other overrides.

* Outliner
    Groups can inspect their collections, change visibility, and add/remove members.

    To change an override of a group collection, you need to select an instance of
    the group, and then you can choose "group" in the collection properties editor
    to edit this group active collection instead of the view layer one.

* Dupli groups overrides
    We can now have multiple instances of the same group with an original "override"
    and different overrides depending on the collection the instanced object is part
    of.

Technical
=========

* Layers
    We use the same api for groups and scene as much as possible.

Reviewers: sergey (depsgraph), mont29 (read/write and user count)
Differential Revision: https://developer.blender.org/D2892

1 files changed, 2 insertions, 0 deletions

diff --git a/source/blender/makesrna/RNA_enum_types.h b/source/blender/makesrna/RNA_enum_types.h
index 155c82bbbc3..345c47ae1bf 100644
--- a/source/blender/makesrna/RNA_enum_types.h
+++ b/source/blender/makesrna/RNA_enum_types.h
@@ -61,6 +61,8 @@ extern const EnumPropertyItem rna_enum_object_modifier_type_items[];
 extern const EnumPropertyItem rna_enum_constraint_type_items[];
 extern const EnumPropertyItem rna_enum_boidrule_type_items[];
 extern const EnumPropertyItem rna_enum_sequence_modifier_type_items[];
+
+extern const EnumPropertyItem rna_enum_collection_type_items[];
 extern const EnumPropertyItem rna_enum_layer_collection_mode_settings_type_items[];
 
 extern const EnumPropertyItem rna_enum_modifier_triangulate_quad_method_items[];