routes: include information on geometry source

[drewda]

RouteStopPatterns will have a geometry_source enum that describes the source and quality of their geometry ({straight lines between stops, shapes, shapes with distances, user enriched geometry}) as part of the additions that @doublestranded and @irees are making in #994

We should also summarize this information on the Route model and include it in the serializer, so users can learn the quality and source of the "representative geometry" on a particular route.

We should also add a query param to the route controller so users can filter for routes with at least a certain quality of route geometry.

This will allow clients like Mapzen Mobility Explorer to chose to filter out routes that only have straight-line geometries.

//cc @meghanhade