The new repository selector UI was using a nonexistant q field to

query the repository API. This often appeared to work correctly because

the selector would end up getting the first page of results, and then

selectize would do the filtering on the client side. If the repository

the user wanted wasn't in the first page of results, they wouldn't be

able to get to it.
While the API does have a name field, that field tests for equivalence

rather than being a search term like the q fields that are part of the

user and group APIs. This change adds a matching q field to the

repository API which does an istartswith query on the name.

Interacted with the related repository selector widget and checked the

  responses in the network tab.
Ran unit tests.