Fix parry logic

[stako]

• Removed med_swing_time variable
• Changed scope of min_swing_time variable to local
• Removed logic for when swing timer is sitting between 20% and 60%
• Corrected logic for reducing swing timer. Previously was setting the timer to main_swing_timer * 0.4, now is reducing the timer by main_weapon_speed * 0.4
• Added logic that a parry cannot reduce the swing timer below 20%

MissHandler is only called when source unit is player or target. Parries caused by other units are not being tracked, which will lead to some discrepancies on the player's and target's timers

[watchyoursixx]

could've swore I pushed this update but it looks like not. Doing it now.