[WIP] Adds 'Find it' link to availability

![image](https://cloud.githubusercontent.com/assets/302258/3859479/0f92250c-1f19-11e4-8f2f-9297a2265e68.png)
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![image](https://cloud.githubusercontent.com/assets/302258/3859495/488ee17e-1f19-11e4-82d1-e66f126a8878.png)
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![image](https://cloud.githubusercontent.com/assets/302258/3860817/0cc6a5f0-1f28-11e4-9932-518160399f11.png)
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![image](https://cloud.githubusercontent.com/assets/302258/3860497/e58e535a-1f24-11e4-86aa-b9e97b1225e8.png)
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- [ ] Add tests
The library code and location code are available via the callnumber already.

https://github.com/sul-dlss/SearchWorks/blob/master/lib/holdings/callnumber.rb#L21-L34