fix(users): extend userList service

and make use of it in mentions
feat(preferences): user prefrences ui
fix(notifications): add styling to notification label
fix(checkbox): Reverted checkboxes to native ones.

SD-688
fix(authoring): update styling for widgets
Merge remote-tracking branch 'ozan/checkbox-fix' into devel
Merge remote-tracking branch 'nikola/devel' into devel