Hopefully fix a rare segfault in MythUITextEdit when using mythmusic. I'm guessing but by no means certain that a linked copy of the string was altered in another thread, e.g. the metadata or playlist load thread. QString uses shallow copies and isn't threadsafe. detaching the string may use more memory but that's preferable to crashing.
Remove theme references to the defunct Set Recording Priorities screen.

This should have been done in SHA1:f8cb433b .