[WIP] Adds 'Find it' link to availability

![image](https://cloud.githubusercontent.com/assets/302258/3859479/0f92250c-1f19-11e4-8f2f-9297a2265e68.png)
--
![image](https://cloud.githubusercontent.com/assets/302258/3859495/488ee17e-1f19-11e4-82d1-e66f126a8878.png)
--
![image](https://cloud.githubusercontent.com/assets/302258/3860817/0cc6a5f0-1f28-11e4-9932-518160399f11.png)
--
![image](https://cloud.githubusercontent.com/assets/302258/3860497/e58e535a-1f24-11e4-86aa-b9e97b1225e8.png)
---
- [ ] Add tests
Also, this will render this partial a lot of times when unecessary.  We should probably have a method on one of the holdings classes that indicates if we should be rendering a stackmap link, and then use that to determine if we should render the partial.  Otherwise we could render this partial hundreds of unnecessary times for locations that we won't show stackmap links for.