CCK layout, CSS and various accessibility work

This pull addresses: https://github.com/opentechinstitute/commotion-docs/issues/28 (css porting from current production site), adds a separate layout for CCK pages, and incorporates an accessibility review of CCK content (properly nested heading tags).

To test, check out branch **issue-28**, run **sudo jekyll serve** from the test.commotion directory and preview content.