[rbp] Make gui limit default to 720 when memory is limited

On a 256M Pi, it's safest to default to 720p gui as memory is quite limited.
[POSIX] fix mount regexp on FreeBSD

same as OSX
[omxplayer] Use macros to reduce diffs with dvdplayer
[omxplayer] Use names closer to dvdplayer
[omxplayer] GetAbsoluteClock like dvdplayer
[omxplayer] Cosmetic: Copy formatting from dvdplayer
[omxplayer] Update master clock changes from dvdplayer
[omxplayer] Update to dvdrefactor
[players] Move Step implementation into PlayerVideo
[players] Make methods protected
[players] Remove unused functions
[players] constify functions
[players] Add plumbing for missing methods for consistency
[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