MythMusic: reinstate the media handler for CD playback

The media handler will detect when a CD is inserted and depending on the
'Automatically Play CDs' setting will either show the music playback screen
and start playing the CD or the tracks will be remembered allowing the user
to manually add them to the playlist either from the Quick Playlists->From CD
menu option or I'll add a node to the playlisteditor screen so they can be
added from there as well.

Note: bumps the ABI so a re-compile is necessary.
MythMusic: Add a CD node to the playlist editor

If a CD is inserted add a node to the playlist editor tree showing the CD's
tracks which can be added/replaced to the active playlist the same as other
tracks.
MythMusic: Add an icon for the CD node in the playlist editor

Themers Note: this add a new 'cd' state to the 'nodetype' statetype in
the button list used for the playlist_tree.
MythMusic: don't flag EOF from av_read_frame() as an error in avfDecoder
MythMusic: rename some variables in avfDecoder to match our coding standards
Merge remote-tracking branch 'upstream/master'