Knockback explosions and fixes (0.0.27)

This update includes a cool knock-back effect on vehicles from explosions and propels objects around in world near it.  Difficulty was re-balanced for police presence and additional fixes to police and traffic AI.  A simple loading animation was also added between game and menu loads.  

Full Build Notes:

• Explosions trigger knock-back on vehicles and objects
• Reduced difficulty and stabilized difficulty by limiting police car spawns to 10-12 on the map instead of being completely variable based on a single probability across all spawn points
• Added loading screen animations
• Fix traffic bugs with overly aggressive drivers ramming into other vehicles continuously
• Fix police searching bugs where police cars would stop and fixate in one spot looking for player after losing sight