Fix to bonus stat-based damage.

Stroke.kod and fire.kod were not obtaining the stat to apply the bonus damage. fire.kod can call its own GetRequisiteStat because it just needs aim but stroke.kod needs to know the stat based on the weapon proficiency. In addition to calling GetRequisiteStat from the proficiency, I've moved the bonus damage code so it runs only if the player is holding a weapon (otherwise it just logs an error in console anyway, not sure if we want this to work with punch).

Scimitar wielding proficiency now has its own GetRequisiteStat function; there is a default agility setting in skill.kod's GetRequisiteStat but I thought it should be in here too. Please correct me if this is not necessary or 'good coding practice'.