Adds prove it buttons to the figure template

Fixes #3376 

@aaronschachter 
A user profile is visible on both `/user/` and `/user/[uid]`.. this link will break in one of those scenarios.  We can use the `l` function with a [fragment](https://api.drupal.org/comment/12934#comment-12934) or use [`global $base_url`](https://api.drupal.org/api/drupal/developer!globals.php/global/base_url/7) to create the full path.

I can also see us having calling this something like `footer` vs `prove_it`, where the `footer` is set to the entire link.  So other galleries that use this template could put other things into the footer section. Does that make sense?