* Add the timeline controller factory to the timeline view model.
In preparation for building a timeline to swipe through media in QuickLook.
* Refactor RoomTimelineControllerFactory.
* Refactor RoomTimelineController.
* Refactor RoomTimelineProvider.
* Add a composer to the MediaUploadPreviewScreen.
And send it's content to the media upload's caption.
* Use the new compound SendButton (updating relative padding in the toolbar).
* Update snapshots.
* Add unit tests for sending a caption.