Use categories in recommendations, remove self.

We aren't really using tags anymore, so we should use categories to
generate the recommended badges. Also, the badge that is used to seed
the recommendations should not be included in the returned list.
Fix self-removal from badge recommendations list.
Test recommendations endpoint, add limit.
Update docs
Merge pull request #170 from mozilla/165-recommend-without-user

Add badge recommendations endpoint (for other badges, not users).
Add newrelic to the badger
Merge pull request #173 from mozilla/newrelic

Add newrelic to the badger
log redis errors instead of silently suppressing them.
Show rubric items in badge detail screen.

Fixes #171.
Badge recommendations stub.
Add api endpoint.
Merge pull request #176 from mozilla/172-dumb-stub

Badge recommendations stub.
Rename method getRecommendations to getSimilar

The method on the Badge model `getRecommendations` was actually getting
similar badges based on the category of a badge. I'm about to implement
the *actual* `getRecommendations` function, which is based on a user's
earned badges history, as well as a handful of other rules.
Fix `for` attribute on a <label>