Latest version as demoed on 8/6
UI, more scenes, guards move

1.  Time limit as defined on GameControl script on main camera.
2.  Privative UI showing remaining Time and status bar showing
proportional amount of zombies (red), humans (white), and dead (black).
 This is basically styled after Plague Inc UI
3. Added “test scene” and “blank scene” for development.  Test has a
single safe zone and human spawn, as well as some guards and zombies
4.  Guards (green squares) now do configurable damage to zombies and
move to engage them.  They can also be killed if they take too much
damage
5.  Refactored some of the scripts to start putting common logic on a
single script