Build Update V_6k7

- Added a new mission, available from the Mercenary Camp- Added a new uniform set, helmet, and back attachment as mission rewards- Introduced a new enemy class (first iteration)- Reworked knockdown logic — now, each damage type (handgun, shotgun, explosives) can trigger knockdown effects on enemies. Enemy classes have varying resistance to different damage types- Applied some fixes to melee; melee logic will move to the next stage of development to make it more enjoyable- Minor changes and tweaks throughout