Bus Plotter III: Client Side Extrapolation and Snap to Path

The bus plotter now "snaps" estimated positions to the appropriate route if they are close enough. I also added checkboxes so you can control whether estimation and snapping are on (this also allows visual inspection of how well they are doing). I wrote all of these in python on the server side first because I know python better and it was easier, but I just finished moving them to the browser. This dramatically decreases the number of requests for bus locations.

Here it is: mbtaplot