First Implementation

Attempt at implementation of an ISystem class, that handles the
IComponent objects and the EntityID to component mapping inside the
System classes.

It is being used in the SimplePhysics and OpenGLSystem class, as well as
implementing SET_COMPONENT_ID(ComponentID) define to be able to set the
Component IDs for the different Components.
Commenting and Bugfix

Commented ISystem and fixed a small bug, that could crash the program if
using getComponent with false informations
Merge pull request #15 from Eldalar/develop

ISystem implementation