Adds result page resource icon, and implements logic for showing icon wh...

Fixes #364 
adds result page resource icon, and implements logic for showing icon when item has more than one resource type

![screen shot 2014-07-08 at 1 59 56 pm](https://cloud.githubusercontent.com/assets/1656824/3516596/d7ec7a1a-06e2-11e4-897c-eaa296f84786.png)

![screen shot 2014-07-08 at 2 00 45 pm](https://cloud.githubusercontent.com/assets/1656824/3516605/f5b9609e-06e2-11e4-951c-8438311341fb.png)


We have a key that we could use for this in the SolrDocument class. https://github.com/sul-dlss/SearchWorks/blob/master/app/models/solr_document.rb#L61-L63

This was primarily used for when we were in the middle of old and new format facets, but could be useful in keeping the solr fields hard coded.