[dvdplayer] Make players pointers rather than objects
[dvdplayer] Create a base class for audio and video players
[dvdplayer] Add dummy hooks in useful places
[omxplayer] Make omxplayer use dvdplayer as base class
[dvdplayer] Use GetTime for scene skipping
[omxplayer] Allow choice of omxplayer through acceleration settings
[players] Remove omxplayer as separately selectable player