Improved AI pathing and other fixes

Hi all,

Updated the game with some fixes:
- Improved AI pathing, the mobs behave less weird when clumped together. This was pretty much the last item in my list of todos for this game.
- Civilians now respawn closer to you when they're outside the screen area
- Mobs are triggered now by how far away from the beach instead of number of buildings crushed



My current high score is 299600, try to beat that. ;-) 

Some players commented the wisdom that you'll need ENERGY UP to rack up a high combo. However this is not necessarily true as there are a couple of other ways to increase your combo meter even if you only have max 5 energy.