Reworked the playlistview,playlisteditorview_tree and playlisteditorview_gallery windows
in music-ui.xml.

modified:   music-base.xml
modified:   music-ui.xml
deleted:    mythmusic/mm_albums.png
deleted:    mythmusic/mm_alltracks.png
deleted:    mythmusic/mm_artists.png
new file:   mythmusic/mm_category.png
deleted:    mythmusic/mm_cd.png
deleted:    mythmusic/mm_compartists.png
deleted:    mythmusic/mm_compilations.png
new file:   mythmusic/mm_coverart_mask.png
deleted:    mythmusic/mm_directory.png
deleted:    mythmusic/mm_genres.png
new file:   mythmusic/mm_info_panel_medium_coverart_mask.png
new file:   mythmusic/mm_no_coverart.png
modified:   mythmusic/mm_nothumb.png
deleted:    mythmusic/mm_playlists.png
deleted:    mythmusic/mm_ratings.png
deleted:    mythmusic/mm_smartplaylists.png
deleted:    mythmusic/mm_years.png