multiple gallery-app bug fixes Bug #907870: [desktop] Gallery does not display photos in sub folders, Bug #1221968: use libthumbnailer for gallery thumbnails, Bug #1268748: videos are not displayed when running on desktop, Bug #1271327: disable switching between camera and gallery on desktop, Bug #1287272: Black flash at the end of the zoom animation" Fixes: 907870, 1221968, 1268748, 1271327, 1287272