CounterAttacking, more hierarchy Clean-up

- WeaponScript is now attached to the tank itself and not a new object
to make it clearer
- removed tank script from tanks since we don't need it yet, haven't
deleted anything though
- Upon a successful shot collision the shot calculates a counter attack
damage and executes it. It doesn't take the counter-attacker's range
into account yet. Also, it doesn't actually shoot a shot back, it just
takes the damage