Load channel settings properly when <cacheindvdplayer> is disabled

There is currently a bug in XBMC which causes channel settings to not be loaded at all when pvr.cacheindvdplayer is disabled. The setting is used to dramatically speed up the time it takes to switch channels on backends with an internal demuxer. The problem is that the call to load the settings is done in a block that is never reached when the setting is disabled.

Because standard files and PVR channels work quite differently I've opted to contain loading/saving of channel settings in PVRManager. Currently they're loaded in Open/CloseLiveStream() and PerformChannelSwitch(). They were previously loaded in DVDPlayer and sometimes stored in Application in addition to whenever the current audio/video settings were changed.

I've also changed the Save/Load methods to take the channel in question as a parameter, this way it is easier to put the call in the proper location. It also alleviates the need to defer to PVRClients to handle the logic.

@opdenkamp @FernetMenta would be nice if you could chip in
@margro can you check for regressions with some backend other than tvheadend/vdr?