stop search: location field and geocoder components

[fpurcell]

We're going to (eventually) need a few changes to the location field to handle stop searches.

I have to validate a lot of the following functionality, but I'm fairly certain we're going to need a few changes in order to deal with stop searches. If you look at the current trimet.org, the geocoder form does two unique things:

1. the geo searching is restricted to searching for just a stops layer (and not addresses, landmarks, etc...). In the Pelias world, this means sending down the 'sources' parameter, ala https://ws-st.trimet.org/pelias/v1/search?text=zoo&layers=stops
2. from the response, we're going to need access to the stop id (and agency id). Pelias (via the transit loader) accomplishes this by encoding stop and agency ids in record id, ala id": "10299::TRIMET::stops", Clients of the geocoder / location field components will need to access those ids, in order to make follow up calls to other data services (e.g., like transit tracker arrival information)

[fpurcell]

Closing this ... fixed along with #13