- Remove not used code
- Fixed some code style
- use a subdirectory in the SDK caches folder, instead of creating another folder directly under caches
- Height of feedback cells only considers attachments that actually can be previewed.
- If an attachment has no source URL and no local URL, don't show it, not even a loading placeholder, don't consider to reserve space in the cell for it
- refresh attachment cache when new data is loaded or one or all message(s) with attachments have been deleted locally
- `feedbackObservationMode` is a property instead of a method
