[pvr] fix internal group loading

As we never load the internal groups from our TV database, changing the group name in our group manager has no effect. This fixes the loading of the internal channel groups.
[pvr] cosmetics: refactor internal group id constants to be more meaningful
[settings] - add new expert setting for enabling ios8 compatibility
[airplay] - implement different announcements when using the ios8 compatibility mode
[airplay] - implemented photo asset cache
[airplay] - send an error code for the fp-setup request
[airplay] - add some handy helpers for using binary plists
[airplay] - handle /play of newer airplay protocols - instead of location it sends 2 seperate entries host + path