Result Gallery view

Resolves #26 

Uses [blacklight-gallery](https://github.com/projectblacklight/blacklight-gallery) plugin but does not include it's CSS and overwrites the gallery views.

Adds functionality for gallery view by enabling default template at `/app/views/catalog/_index_gallery_default.html.erb`

Object specific views can be generated following the current pattern eg `_index_gallery_file_collection.html.erb`

Button placeholder for preview functionality also included.

![screen shot 2014-06-10 at 3 51 38 pm](https://cloud.githubusercontent.com/assets/1656824/3238115/feab1ece-f0f1-11e3-94fa-ab7393b8ef16.png)

![screen shot 2014-06-10 at 3 53 25 pm](https://cloud.githubusercontent.com/assets/1656824/3238120/1255615a-f0f2-11e3-8e5f-2b03f8c6b53c.png)
Ideally as a feature test this would click on the gallery button from a default search result view.