close #2543

Fixes #2392: Added `addCssStyle()`, `removeCssStyle()`, `cssStyleFromArray()` and `cssStyleToArray()` to `Html`

fixes #2519: MessageSource removed translation messages when event handler
was bound to `missingTranslation`-event

allow extending only one class to add scopes, fixes #2146

TODO:

- [ ] adjust guide docs
- [ ] adjust README files of extensions
- [ ] finish work and fix test breaks

Fixes #2360: Added `AttributeBehavior` and `BlameableBehavior`, and renamed `AutoTimestamp` to `TimestampBehavior`

fixes #2265

Fixes #1186: Changed `Sort` to use comma to separate multiple sort fields and use negative sign to indicate descending sort