VideoConfig: Rename Separation to Depth and update descriptions.

More accurate since it's not a real IPD and Nvidia also calls it depth.
GeometryShaderManager: Boost convergence value.

Most game don't require much granularity regarding the convergence value.
The default convergence was also too low, this commit increases it tenfold.
VideoConfigDiag: Enable stereoscopy options.
VideoConfig: Rename "StereoMonoEFBDepth" to "StereoEFBMonoDepth"

Makes a little bit more sense.
VideoConfigDiag: Don't enable the post-processing config button when there are no options.

The handling of the Anaglyph override was incorrect.
Merge pull request #1766 from Armada651/enable-stereo

Enable stereoscopy settings.