CYB-323 User likes/dislikes only count *once* per gallery item

* By tracking all activity to likes/dislikes, all actions were being counted in the return counts for gallery/index action,
   and so also on the displayed gallery page.  Instead, only count each person's action once.

[CYB-323 User likes/dislikes only count *once* per gallery item](https://jira.ets.berkeley.edu/jira/browse/CYB-323)