Add CUSTOM_MOTOR_VEHICLE to StreetTraversalPermission. Add tests.

Adds a StreetTraversalPermission for custom motor vehicles like trucks, motorbikes. This way we can configure the graph to allow/disallow these vehicles on certain roads.

Additionally:
1) Format StreetTraversalPermission.java
2) Add unit tests.
3) Make it more explicit that StreetTraversalPermission is a bitset.

Everything builds, tests all pass (including new ones).
Avi