[API] add priority in chapter create and update
[API] add priority in page create and update

Kept existing "COMMENTED_ON" activity for upgrade compatibility,
specifically for existing webhook usage and for showing comment
activities in activity lists.

Precursor to content notifications.
Currently untested.
Also applied some type updates.

Includes testing to cover.
Also added file missing from previous commit.

Added DB and started controller method.

Got watch system working to an initial base state.
Moved some existing logic where it makes sense.

Put together an initial notification.
Started logic to query and identify watchers.

Also rolled out watch UI to chapter and page views

- Adds option filtering and alternative text for page watch options.
- Adds "Watched & Ignored Items" list to user notification preferences
  page to show existing watched items.

- Added general user preferences view and updated link in profile menu
  to suit.
- Made notification permission required for notification preferences
  view, added test to cover.

- 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.

Covers core case scenarios, and check of notification content.

- Added titles for preference pages.
- Added extra check for non-guest for notifications on preferences page.

- Ensured watch options passed in all meta template usage to fix failing
  scenarios where watch options did not exist.
- Fixed testing issue caused by guest user permission caching.

Added test and changed logic to properly check the view permissions for
the notification receiver before sending.
Required change to permissions applicator to allow the user to be
manually determined, and a service provider update to provide the class
as a singleton without a specific user, so it checks the current logged
in user on demand.

…cations

Content user notifications

Updated status endpoint cache check to include a random component in the
key to avoid conflict during simultaneous checks.
For BookStackApp#4396

Review of BookStackApp#4313
- Made constructor changes while reviewing some classes.
- Updated API examples for consistency.
- Tweaked formatting for some array changes.
- Simplified added tests.
- Tweaked chapter/page repo priority handling to be simpler.

Performed manual API endpoint testing of page/chapter create/update.

Upped from text to medium text.
Aligns with modern Laravel default.
Fixes BookStackApp#4453 where were reaching the limit of TEXT.

For BookStackApp#4429

Adds just the part to store image data, and remove on successfull save.
Alters save events to properly throw upon error.
Adds IDB-Keyval library for local large-size store.
For BookStackApp#4421

- Tweaked wording of popup title.
- Updated WYSIWYG create handling to properly remove drawing container
  on failure.

Tested across FF and chrome, in both editors for create & editing.

…_store

Browser-based drawing backup storage system

Prevention of action on certain routes for guest user when public access
is enabled. Could not see a way this could be a security issue, beyond a
mild nuisance that'd only be visible if public users can edit, which
would present larger potential nuisance anyway.

Included unit tests to cover validator functionality.
Added to webhooks.
Still need to do testing specifically for webhooks.

- Covered webhook SSR allow list useage via test.
- Updated allow list handling to use trailing slash, or hash, or end of
  line as late anchor for better handling for hosts (prevent .co.uk
passing for .co domain host)

Added min-height to flex elements to ensure they properly flex within
the container rathen than adjust to content.

For BookStackApp#4466

For BookStackApp#4474

- 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 BookStackApp#4501

- Passed decode flags to provide consistent behaviour across PHP
  versions during testing.
- Added env option to prevent local option taking action in PHPunit
  tests.

Fix typos

…anguage

Notifications: User language for notification text

- Adds filtering to the watched items list in notification preferences
  so that deleted (recycle bin) items are removed via query.
- Adds relations and logic to properly remove watches upon user and
  entity delete events, to old watches in database do not linger.
- Adds testing to cover the above.

Did not add migration for existing data, since patch will be close to
introduction, and lingering DB entries don't open a security concern,
just some potential confusion in specific potential scenarios.
Probably not work extra migration risk, although could add in future if
concerns/issues are found.

Related to BookStackApp#4499

Improved wrapping and flex control to prevent button text force wrapping
to newlines.

For BookStackApp#4502

Could error upon div elements without classes, including drawings.

Related to BookStackApp#4510 and BookStackApp#4509