Add inputmultiplexer to gameScreen

In order to use two different types of input listeners, we need to use a
multiplexer.

*note, the reason we need two kinds is to handle the differences between
pc and android.
Better way to zoom

Zoom should not be a solid number, but a number that depends on the
distance crossed between fingers.
Merge branch 'master' of https://github.com/DranoMax/AntSim