Adding support to only show appropriate languages on supported services

This change introduces a dictionary which maps docs to languages. I'll make the list fully functional when we are confident in this approach.

Relevant changes are at https://github.com/rackerlabs/developer.rackspace.com/compare/dev...gh-206#diff-c669c82f2dfb340df8af5584cb9ad589R4

- Fixes #206
Ahhh! @ycombinator beat me to it by a few minutes. I saw this and thought it could be extended slightly to fix #226. It's either that or having a separate layout just for the /docs landing page that is missing the language list.