Refactored MeshManager into AssetManager/MeshProcessor

First steps towards Component/Entity system, gave responsibility for
loading to AssetManager class, rendering to MeshProcessor class.
Input: Xbox controller class finished, testing needed

Changes: Finished button press methods, added deadzone calculations,
normalised output from non-boolean methods, added vibrate method.
Testing is now needed.
Mouse: Added enums

Enumerated type for mouse buttons, uses virtual key as value;
Keyboard: Added enums, started button press methods

Added enums for key state, started code for detecting keydown, keyup and
hold events.
Input: Finished method for registering keyboard