Add support for Players, victory and draw. Refactor globals away.

Add a Player interface, with InputPlayer implementation (can receive input - say by keyboard or network - from a channel) and two random AIs that do nothing.

r: @alexcoco 

![bomberman_players](https://f.cloud.github.com/assets/1189716/2300872/c5256122-a110-11e3-8e17-79b1f259d3b4.gif)