add strings for unknowns
 don't filter unknown artists/albums and show them on top of lists

Conflicts:
	JMPDComm/src/org/a0z/mpd/Artist.java
	JMPDComm/src/org/a0z/mpd/MPD.java
	JMPDComm/src/org/a0z/mpd/Music.java
show unknown album text in album grid, too
show unknowns in search results, too
show "Unknown Artist" in SongsFragment header
don't list unknown albumartists for "unknown artist"