Removed System Manager, as with the new design choices it is unnecessary.

Removed all references to system manager and its includes from the codebase.
Cleaned up Renderer class a bit.
Removed active shader program pointer from Renderer as it is unnecessary.
Removed Text Rendering code from Renderer as it is now served by the mesh generation class combined with mesh rendering functions.
Created a new class called TextureManager that will eventually replace the static code in Texture.
Fixed the memory leak with vertexdata by using free().
Created a shutdown call in Renderer that handles cleaning up the internal renderer structures.