CYB-338 & CYB-339.  Changes to Gallery API to accelerate response.

*  WIP.  This will pull all the data via SQL, and not need to iterate
     over the result set.  The only Ruby manipulation is a single merge
     of the comment data into the single (#show) view for a single gallery item.
* Adds a #show view at /api/v1/gallery/:gallery_id

https://jira.ets.berkeley.edu/jira/browse/CYB-339
https://jira.ets.berkeley.edu/jira/browse/CYB-339