ArtistAlbumsWidget, ArtistAlbumWidget, DiscBox: Migrate to use Gtk.Template
Migrate ArtistAlbumsWidget, ArtistAlbumWidget and DiscBox so that they use Gtk.Template
Edited by Apostol Bakalov
Migrate ArtistAlbumsWidget, ArtistAlbumWidget and DiscBox so that they use Gtk.Template