Add support for selection of album cover. Can use image from gallery or upload a new one.

 - Updated version to 1.5.3-a2 for package install purporses
 - Add new field to galAlbum model - cover_filename

Signed-off-by: Egor Bolgov <egor.b@fabricasaitov.ru>
Merge remote-tracking branch 'splittingred/pr/266' into pr-266