Add video controls for animated images (e.g. gif-s)
Changes RasterImageViewAdapter to have a HUD similar to VideoViewAdapter's (in fact, a large portion of the code was copied and adapted from there), and also updates Document and AnimatedDocumentLoadedImpl to support toggling play/pause and seeking to a specified frame.
I also experimented with using VideoViewAdapter for .gif images, but opted to reimplement the video controls in RasterImageViewAdapter rather than reimplement image scaling/zoom/etc. in VideoViewAdapter.
BTW, this MR was made during a livestream, starting at 3:50:36.
Edited by Bojidar Marinov