Intersection not implemented as a heap

[sss04]

Streets currently store intersections as a list:

ai-traffic-control/sim/street.py

Line 14 in bd606c6

self.intersections = []

This should be changed to a heapq to allow sorting. When it is, the below code should be changed.
The below code also assumes only one intersection - which is not generalizable.

ai-traffic-control/sim/world.py

Line 28 in bd606c6

lastIntersection = street.intersections[0] # TODO actually get the last intersection once it's a heap

ai-traffic-control/sim/car.py

Line 96 in bd606c6

nearestIntersection = currStreet.intersections[0] # TODO(sssai) actually get the nearest intersection once it's a heap