* rename wps_engine to skin_engine as that was agreed on
* rename music_screen back to wps
* clean up the skin display/update functions a bit
* make skin_data_load setup the hardcoded default if a skin cant be loaded for whatever reason instead of doing it when it is first displayed
ignore any gui_wps or wps_ or gwps_ nameing in skin_engine/ ... these will be renamed as this work gets finished
git-svn-id: svn://svn.rockbox.org/rockbox/trunk@22135 a1c6a512-1295-4272-9138-f99709370657
