Port dav calendar settings page to Vue.js

- Drop reliance on deprecated global jQuery object.
- Allow testing user interactions.
- Use newer technology stack.

---

Test user interactions with the groupware dav settings

Add infrastructure to test Vue components:

- Use recommended libraries:

    - https://vuejs.org/v2/guide/testing.html#Recommendations
    - Use jest-dom for robust assertions on the DOM state
    - Use user-event to be more representative of user actions

- Code is transpiled by Jest, with the help of vue-jest.

Ignore test files for no-unpublished-import. Prevent ESLint from
flagging:

```
/home/runner/work/server/server/apps/dav/src/views/CalDavSettings.spec.js
Error:   1:24  error  "@testing-library/vue" is not published         node/no-unpublished-import
Error:   2:23  error  "@testing-library/user-event" is not published  node/no-unpublished-import
```

Signed-off-by: François Freitag <mail@franek.fr>

1 files changed, 1 insertions, 0 deletions

diff --git a/build/files-checker.php b/build/files-checker.php
index cd26499e899..88006e15a63 100644
--- a/build/files-checker.php
+++ b/build/files-checker.php
@@ -37,6 +37,7 @@ $expectedFiles = [
 	'.idea',
 	'.jshintrc',
 	'.mailmap',
+	'.npmignore',
 	'.php_cs.dist',
 	'.scrutinizer.yml',
 	'.tag',