Evaluate how edits affect connectivity

[dabreegster]

Problems today:

1. You can make edits that cut off a bus stop or mess up a bus route. This crashes right now.

2. Some edits might cut off parking. (And also, existing parking lanes along the boundary of the map are "blackholed" today, but that isn't clear in the game UI at all.)

3. Edits could disconnect the graph for different vehicle types, or fail to re-establish connectivity intended. For example, when changing construction lanes along the west seattle bridge to driving lanes, it's easy to miss a few small roads in the middle.

Need to think through what should be outright banned, what should be warnings, how to surface this in the UI.