Mobs can now migrate cities

TO ACTIVATE unit test,

1) Make some basic towers [press 1 to select basic tower]
2) control click like  you are creating track. Mob will be sent to all
other towers like complete graph, and the spawning of patrol will begin
3)  Wait for some mobs to spawn.
4)  Control click again, and the tower that was placed last should
receive all but the newest spawned mobs.

The tower handler contains code to transfer cities.
TDPanel.getMobHandler().sendTroups(t1.getID(), t2.getID());
is the line in specific where t1 is start city and t2 is destination.