Store stops buffers, calculate buffer coverage indicator

Calculates the ratio of a union of buffers around GTFS stops within the city boundary area, with the area of the city boundary area itself. Also stores the calculated buffer in the database so that it can be displayed by Windshaft.
This was the culprit for the issue you were having with the suburb ratio earlier. Short of writing up an endpoint for verification of our names (which just isn't worth it), I think this warning is our best option.