Adding RunModes.

Removing the createScene function from the application and moving that
functionality into the RunMode where it should be.

Admittedly, this module is in need of code review, but it's important that
we at least have a framework out there. Here are some points I'd like to
come back to:
  * RenderWindow - how this is created an propogated to the various places
      it is needed around the application.
  * Initialization of RunMode - Make the interface between
      NimbusApplication and RunMode a bit cleaner by standardizing the
      creation and initialization of RunModes.