Big update!

A lot of things have been redone so I'm just gonna run down some basics.
Collision has been remade. Now the Overworld hero class contains a
boolean array that keeps track of all the adjacent gridsquares, if the
player tries to move into an occupied square the player will stop.

The Filemap reading has been improved to work better. The array that
keeps track of the grid is now in the same coordinate system as libGDX.

A Constants class has been added to keep track of different kinds of
gridpieces. P for Plattform and O for air/void