Catch bot.poll_action() exceptions and state.kill_unit()

[ArielHorwitz]

The battle calls bot.poll_action() and at that point excecution is passed to the bot code. Unhandled exceptions in this execution will crash the program. I suggest we try..except the call to catch any exception and log the entire traceback.

If an exception is caught, I suggest the battle by default should use a (yet to be written) method in State State.kill_unit which will... Kill the unit.