- This ensures content notifications are not translated to receiver
language.
- This adds actual plaintext support for content notifications (Was
previously just HTML as text view).
- Shares same base class across all mail notifications.
- Also cleaned up existing notification classes.
Future cleanup requested via #4501
- Updated mail notification design to be a bit prettier, and extracted
text to new lang file for translation.
- Added debounce logic for page update notifications.
- Fixed watch options not being filtered to current user.
