Fix blocking

This fixes martial arts blocking by replacing the "can_leg_block" value with two separate ints, "arm_block" and "leg_block" that determine the unarmed combat levels at which a player may arm and leg block with a given martial art respectively. Currently weapon blocking is set up as a subset of arm blocking, so players will only block with their weapons if they could normally block with their arms.

This also removes a bunch of old is_style() function based stuff since it no longer applies to the new martial arts (since they will never be in your inventory).