V6 - Sound and trains fixed

V6 adds some fixes to audio which had been removed from v5 due to bugs.

Traffic now has sounds, and luas and darts should now move along their intended routes.

Have added another variable to the different birds, energy use, meaning a larger bird now has a balancing benefit, it uses less energy, as opposed to just being slower and heavier than the others.

Also added some cranes to the city as they were missing from the docklands area.