Feature/stable repo links

Hi @barnabyalter 

All tests are passing here now, but deploying this will require incorporating the companion pull request in the findingaids_ead repo and deleteing/reloading tamwag/tamiment, archives/universityarchives, bhs/brooklynhistory, and nyhs/nyhistory.

I had one question, which I'm including as an inline comment in the code below.

Let me know if you have questions or comments

cc @NYULibraries/finding-aids 
@chrpr Good catch with the 'url' field here, but instead of changing the directories we're looking at you can just change the url field in the `repositories.yml` and then add an `:as` statement:

```
get "#{coll[1]['url']}" => "catalog#index", :search_field => "#{coll[1]['display']}", :repository => "#{coll[1]['display']}", :as => "#{coll[1]['admin_code']}"
```

This will generate all the `tamiment_url` etc helpers.

Changing the directories in the EAD repos requires work from the DLTS guys as well so we can just leave that out of here