[3D] Support switching to 3D resolutions

Include matching 3D flags (SBS/TAB) in the score of a resolution to switch to, to enable switching to 3d modes.
Also remove the old code that treated 3D modes differently when assigning a score.

I've also added a small weight to higher multiples of the desired framerate, so if display supports 30, 60 and 120Hz
and the video is 30fps then 30 will now be chosen rather than 120. This reduces the overhead of rendering the gui.

This reinstates auto switching to 3D mode on the PI that was lost in the stereoscopic update.

Note: This is an RFC.
I'm sure choosing the smallest frame multiple will be contentious, but this is a starting point for discussion.
@elupus?