Add a site map to the app

[brundonsmith]

We should create a new dedicated Map tab, to help people find their way around the grounds. An interactive, zoomable map via something like Mapbox would be ideal. But in the short-term, it could make sense to just put an image of a labeled map in there and let the user scroll and zoom that.

Features that we'd love to see:

• Pins/labels for major "named areas" like the big top, cafeteria, etc (partially enumerated in the event_site table)
• Integration with the events UI- maybe you can click on an event location and be taken to that pin on the map
• Maybe the map itself shows currently-ongoing events as pins on the map