Kaiju Engine (issue #22) - Hook up the mouse input events for X11

This is working X11 mouse input events. There is also a bit of refactor for the windows mouse events here to make more common code between the windowing systems. I refactored the windows code so that which button was being clicked is being sent rather than just X1 and X2

https://github.com/KaijuEngine/kaiju/pull/24