Optimize route traces

[thekaveman]

Currently, when a particular route map is viewed on the BBB site, e.g. Route 14, a 1.4mb traces.geojson file is downloaded to draw the route trace. This file contains traces for all routes, each of which is loaded into Google Maps as a hidden layer, and selectively shown for the route in question.

This download can be problematic for mobile customers, especially on slower connections.

We should try to optimize the route trace download similar to how stops are handled, and only request the trace for the route in question.