Revise map selection feedback

[bbradforddesign]

The current method used to provide user feedback is to mount a new geojson object over the original, with only the selected zone visible. This is pretty inefficient compared to modifying the original geojson's styles, however it will work as a stopgap for the moment. The docs mention a 'foreach' method that can add a listener to each feature in a geojson, which would let us modify the style on a specific feature directly on a click, however it doesn't exactly specify how to do this, and is pretty cryptic overall. Anyone feel free to take a crack at it!

If possible, we should also add a popup on the map stating which zone is selected. This shouldn't be very intrusive, and would give a big boost to usability.