decouple the main logic class from the main window class

[RiedleroD]

It'd be nice not having to fear that some weird window member could get overritten by a new logic member.

It should be split like so:
The new class MainWin() will go into the CONSTANTS.py file, along with its invokation as win and the constants that get set regarding window size. The new class MainLogic() with most of the members and functions from the current GameWin() will stay in the main.py file.

[RiedleroD]

implemented