Add OAC finding aid links from the index for merged collections.

Closes #161 

In addition to the search results view I added the finding aid to the collection masthead and the "In collection" access panel.

### Masthead
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![finding-aid-masthead](https://cloud.githubusercontent.com/assets/96776/3196014/04ab7452-ed20-11e3-9787-acc434048e82.png)

### Search result
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![finding-aid-search-result](https://cloud.githubusercontent.com/assets/96776/3196015/0c426a72-ed20-11e3-9023-5c4102e638aa.png)

### In collection access panel
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![finding-aid-in-collection](https://cloud.githubusercontent.com/assets/96776/3196017/135a48b6-ed20-11e3-8b50-92bc8304f8bc.png)