Update to traffic dependency system

[mxgrey]

This PR updates the fleet adapters to use the new traffic dependency system of RMF. Read more on the new system and its benefits here.

For the fleet adapters, the API remains exactly the same, with just these notes to account for:

• The original TrafficLight API is now completely removed. Relative to the new dependency-based system, the old traffic light system was unreliable. Besides it was so difficult to use that I don't believe anyone was using it anyway. The EasyTrafficLight API remains exactly as-is, but should now behave much better since it has been reimplemented to use the new dependency system.
• The "Full Control" API [1] [2] remains exactly as-is, except you no longer need to wait at the time specified by the plan waypoints given to the command handle. When you receive a new path, your robot can just follow the path all the way to the end. The waypoints given to the command handle will cut off at any waypoint that has a risk of leading into a conflict.

This PR depends on:

• Create an AssignID utility rmf_utils#23
• Introducing the traffic dependency system rmf_traffic#70
• Introducing the traffic dependency system rmf_internal_msgs#37

[aaronchongth]

Ran the same test scenarios without seeing any issues so far, this is awesome! LGTM