User preference 3D display options tweaks

* Change label in the user preferences to "3D Stereo Display" because we support only stereo displays at the moment
* Remove "None" 3D Stereo Display
* Rearrange items in eStereoDisplayMode to alphabetical order (the same order they are in rna_userdef.c)
* Anaglyph became the default; I think this is good default because I guess this is the most popular method for viewing 3D stereo on typical computer monitor
* Some small cleanups: change one //-style comment to /*-style (because this is what's used in other places to comment out EnumPropertyItem lines), comment out S3D_DISPLAY_BLURAY in eStereoDisplayMode enum

Resolves #41