Joint is now drawn only by World

Make Joint becomes an abstract class.
Add drawLabel() to Joint.
SourceJoint can now blink! (updateBlink()).
Rewrite some interface between Joint, RoadEnd, and Road

Now RoadEnd always keeps a copy of outwardLane and inwardLane.
Huge update, I don't know how to say

Main update: Vehicle can now drive to another random adjacent lane when
reaching the road end.

Driver AI coming soooooon!