Fixed up so that catalog detail works.

 - Added the missing catalog.html template
    - This is quite minimal, and currently just contains the same
      info as on the summary page, but could be extended to contain
      more useful info (# datasets etc, software/version used)
 - Fixed the typo (re-assigning catalog) for the catalog route
 - Fixed hiding of keywords/group with no name.
Merge pull request #20 from okfn/template-fix

Fixed up so that catalog detail page works.