added Assimp model loading library functionality

Now using glm::vec's to initialize OpenGL vertex etc.
buffers. Changed layout of Mesh to more closely
resemble Assimp (with multiple subMeshes). Added
IMesh base class to handle rendering of each
mesh type. Removed math classes because
they are no longer being used. They may return
in the future if needed. Removed unused
variables in the RenderFramework class. This class
will be changed to a namespace soon.