Add acorn file for watermark, and RELEASE scheme
Update notes
Minor improvement to detail sizing
Rewrite gallery detail title setting mechanism to use a var scrollPageIndex instead of using a debounced title update callback
Debounce GalleryDetailViewController::updateScrollPageIndex to reduce CPU use
Integerize the watermark rect
In gallery detail collection view, preload renderings of drawings to left and right of current drawing, so user doesn't have to wait for the drawing to load when paging.

- required additions to CancelableAction<T> to have a convenience constructor with no done handler, so a done handler can be assigned later
- required addition of animate:Bool property to ImagePresenterView
- for code cleanup, added count:Int property to BasicGalleryCollectionViewDataSource which returns number of drawings
Merge branch 'feature-gallery-detail-preload'