Refactor follow/unfollow button AJAX

Rather than re-rendering the entire view and manipulating the dom upon a
successful follow/unfollow request this moves the follow buttons (for
the show view and the partial) into a partial and renders them upon a
successful follow/unfollow then inserts the results into the dom.
Merge pull request #626 from opscode/follow-button-refactor

Refactor follow/unfollow button AJAX