Add full call number browse

Closes #28 

Addresses much of the needs of #29 as well

**Note:** This won't work on a local index.  The sort keys that need to be generated and indexed in order for solr to return the call number browse appropriately will be completely unwieldy to manage locally.  View any index w/ lots of MARC records (production would be best) to get a good callnumber browse.

I filled in the simple stub panel for call number browse w/ links to the full browse for now until we address #29.

### Record view
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![cn-browse-record](https://cloud.githubusercontent.com/assets/96776/3262851/829c03fa-f26a-11e3-9db9-a819cd606e06.png)

### Browse view
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![cn-full-browse](https://cloud.githubusercontent.com/assets/96776/3262854/88b7c026-f26a-11e3-9d09-ada3c5168a82.png)
If which item is not found?  We should never get to a callnumber browse from a start parameter that does not exist.

`NearbyOnShelf` shouldn't return any non-existent items theoretically so everything that gets retuned in `#items` should be a SolrDocument hash.