More post-processing options: different post processing modes per video

**2011.Oct.12** Updated for no conflicts with master.

Post-processing all videos with high quality pp filter combination 'ha:128:7,va,dr' makes videos too blurred. Not all videos need so much vertical/horizontal de-blocking. From experience with MPlayer's video filter settings I would suggest the following changes:

Introduce 3 PP Modes that can be switched in the GUI and saved per video:

- Default: 'ha,va,dr' (this is accurate but not too aggressive and it is based on FFMpeg default that is 'hb:a,vb:a,dr:a', only changed horizontal/vertical deblocking to accurate and disabled auto switch-off flag). Because this is the mode that can be overridden in xml, advanced users with own pp settings won't be affected by this change.

- Aggressive: 'ha:128:7,va,dr' (high quality but not suitable for all videos this is FFMpeg high quality pp filter combination 'ha:a:128:7,va:a,dr:a' without the ':a' flag)

- Auto (slow CPU): 'hb:a,vb:a,dr:a' (FFMpeg's default setting that automatically switches the subfilters off if the CPU is too slow)

See: http://trac.xbmc.org/ticket/11556

@elupus: libavfilter was put in place but the currently integrated version does not have a filter named 'mp' so we could use what we have now until ffmpeg will be updated.