New mission added and improved teammate AI

- Added a new hostage rescue mission that takes place at a riverside with yachts
- Improved the teammate AI
- Fixed a nasty bug that was causing the gun sights to be misaligned when aiming down the sight
- Tweak the enemy Time to Kill
- Improved the particle FX for various effects
- Tweaked the difficulty of various missions
- Fixed a bug that was causing some missions to start before the player even arrived.
- Improved the visual FX for the hostage cutting minigame
- Fixed a nasty bug that was preventing players to interact with objects after they died with a shield.
- Improved Sound FX for various guns and enemy weapons