AlbumArtImages: add option to not load images from the database
Myth Protocol: add a MUSIC_FIND_ALBUMART command

This command will find the album art in the same directory as the track and
also look for any embedded album art in the tracks tag.

Format: MUSIC_FIND_ALBUMART <hostname> <songid> <update_database>
AlbumArtImages: add a scanForImages() function

This sends a MUSIC_FIND_ALBUMART command to the BE to find any directory and
embedded tag images for a track. The command is sent in its own thread so it
wont block the UI thread.
Merge remote-tracking branch 'upstream/master'