Made attack type capitalisation consistent, started shift of attack type logic from responder.php to BMAttack.php
Added function BMAttack::possible_attack_types($attackers) to list all possible attack types that the attackers can perform
Shifted possible attack finding into BMAttack::valid_attack_types($attackers, $defenders)
Shifted logic for valid attacks from BMAttack into BMGame. Added unit tests.
Completed unit tests for BMGame::valid_attack_types()
Added unit tests for valid pass attacks
Added unit tests for in-game shadow attack