Edits to resizing and tons of minor changes.

Resizing pulled out of event loop and simplified.  
Control class keeps track of scale factor and recalcs it on window resize.  
This scale factor is to be passed to the `scaled_mous_pos()` function.  It is also passed to state event and update methods.  
global variables `prepare.SCREEN` and `prepare.SCREEN_RECT` have been removed.


-Mek