Updated Czech translation
Add several picture type strings

Improve the heuristic for guessing the image type from the filename.

https://bugzilla.gnome.org/show_bug.cgi?id=740654
Add skeleton MusicBrainz search dialog
Add skeleton MusicBrainz query context
Add simple asynchronous query support

Use GSimpleAsyncResult to dispatch MusicBrainz queries from a thread, in
order to keep the UI responsive.