Gameplay improvements

Fixed:
- Clunky combat animations. Combat, in general, should be more fluid now.
- Some minor bugs.

New features:
- In close combat, a hit can push an enemy. Probability depends on the enemy stamina.
- When you block a front attack, the enemy can be kicked and pushed forward.
- New hit reaction animations.
- In a hopeless situation, AI can drop a grenade.

The overall balance was reworked. Now bots are tough in close range combat so you need to be smarter. Use grenades and sprint-push to eliminate your enemies.