Add next bus widget

[stephenyeargin]

Two destinations:

• next bus to Five Points
• next bus to the Nations

Ideally, all of this would be configured by way of selecting a particular route (and direction) as part of the "collection" for a widget to measure off of.

Example:

• Show next bus that uses the 4 or 20 route (that takes you to Five Points or through the Shelby area)
• Grabbing those two routes, reduce those down to the "next bus that leaves the MCC going out on those routes" and show a countdown timer.

Stretch goal:

• Show the timer with color-coordinated "meter"
• 20+ minutes = green
• 10-19 minutes = yellow
• < 10 minutes = red

Data source:

• Use https://gist.github.com/jameswhite/be251a2dfe7f33dec18f as a data source
• Parse with gem found at https://github.com/nerdEd/gtfs

[stephenyeargin]

^^ @brandonvalentine @jameswhite seems do-able.