Resolve "_ExtensibleModelBase's meta check does not work"

Closes #1217

See merge request !1729

Resolve "Migrate management of OAuth applications to CRUD list"

Closes #1201

See merge request !1717

Resolve "Migrate announcements management to CRUD list"

Closes #1200

See merge request !1709

Resolve "CRUD-List's edit-item has extraneous fields"

Closes #1210

See merge request !1730

Add an optional minimal-patch-mode to the ObjectForm

See merge request !1731

In this mode the patch send to the backend contains only what the user
actually changed. This works the same way as the InlineCRUDList
creates patches.

It is not enabled by default, because it could maybe break some
nonstandard DialogObjectForms.
It should become the prefered option.

Merge remote-tracking branch 'origin/master' into 1200-migrate-announcements-management-to-crud-list

Merge remote-tracking branch 'origin/master' into 1201-migrate-management-of-oauth-applications-to-crud-list

Resolve "[CalDAV] MultipleObjectsReturned at /dav/calendar/personal/"

Closes #1216

See merge request !1728