Allow customizing short label for route on MapSpider component and Isochrone map

[youngj]

Currently the MapSpider component displays the route ID for each route near where the user clicks. However, some routes have a route ID that is not meaningful to a user. For example, the Portland Streetcar NS line has the route ID 193, and the MAX Green Line has route ID 200. There should be a way to customize the short label for certain route IDs in the agency configuration YAML (e.g. /backend/agencies/trimet.yaml). This could be configured via js_properties so it is sent to the frontend without necessarily needing to store it along with the route configuration in S3. Then the MapSpider component could display this label if it is available instead of the route ID.

The same issue applies to the isochrone map in the list of routes and when displaying trips between two points.