Explore Routes that span multiple neighborhoods

[misaugstad]

Brief description of problem/feature

To speed up implementation, we made it so that RouteBuilder only lets you explore routes that are contained to a single neighborhood. It's a weird restriction from a user's perspective, so we should work on how to remove the restriction!

It's complicated because all the way up the chain, we assume that you are exploring in a single neighborhood. We show a map of the neighborhood on mission complete, there are checks throughout the Explore page code to see if you've completed the neighborhood you're in, the mission table has a region_id field, we scale the length of your missions based on how many you've completed in the given neighborhood, etc.

It's certainly doable to make this change, it was just worthwhile to handle it completely separately from the initial RouteBuilder release.