Make client-side refresh rate configurable via URL parameter

[barbeau]

Summary:

We're looking at using the USF Maps App on TVs in display lobbies. As part of these installations, we'd like to increase the client/server refresh rate for items like the USF Bull Runner to show the vehicles moving on the map more smoothly.

TODO:

• [ ] Check to see how frequently we're currently refreshing Bull Runner positions
• [ ] Make this configurable via URL parameter, but with a lower threshold that doesn't exceed the GTFS-rt VehiclePosition source feed

[barbeau]

From @liquidsunshine, regarding priority of some of these related issues for using the app to show information in the CUTR lobby on a TV display:

Here’s how I would prioritize them, based on CUTR’s needs:

1. https://github.com/CUTR-at-USF/usf-mobullity/issues/401 (a bug)
2. https://github.com/CUTR-at-USF/usf-mobullity/issues/403 (allows us to automatically center on CUTR)
3. https://github.com/CUTR-at-USF/usf-mobullity/issues/404 (allows us to automatically bypass popup)
4. https://github.com/CUTR-at-USF/usf-mobullity/issues/405 (offers a better view of CUTR)
5. https://github.com/CUTR-at-USF/usf-mobullity/issues/402 (possibly improves refresh performance)