add fundamentals for the selection logic (WiP)
This adds a second draw pass that draws a second image resource on the renderer that is not visible to the user. It will but will only be used to identify objects, walls and tiles on the screen by drawing each individual entity with a unique, single colour.
Once a mouse click is registered, a copy of that image is made to CPU readable memory in order to check the unique (RGB) colour at the given pixel coordinates. However, so far nothing is actually done with this information.
