Add support for type constraints on suggest

[zang0]

When we add entities beyond regions, like diseases, etc, we'll probably want to constrain by type as well, something like:

http://odn-backend.herokuapp.com/suggest/v1/entity?query=seat&limit=10&type=region

for now I think its not pressing so feel free to punt if its more than a few minutes to impl.

[aaasen]

There isn't a way to do this using the Socrata autosuggest API, so I would have to either make a separate autocomplete dataset for each region type or pull down results from the main entity autosuggest dataset and then filter them. Neither solution seems optimal so I'm going to punt on this one.