Added DRM options. See comments.

Added options for steam, desura, gog, and DRM-free.

Suggest not using GOG as a filter unless/until more than one game has GOG keys (currently only retro city rampage).

Only 10 items support desura, so...?

In any case, worth leaving these in there even if not used, so they can be added later if need be.
oops. Took out the var init for a viewer, forgot to put it back.
RCR gog edition most certainly does NOT come on steam. It comes on GOG, of course.
Merge pull request #22 from Efreak/gh-pages

Added DRM options to games.js.