Migrate to moderngl_window

[einarf]

We are merging the demosys/context windows and moderngl/examples/window packages picking the best from each into a separate package. This way we don't have to re-invent the wheel for every single project when it comes to dealing with context creation.

moderngl/moderngl#292

[einarf]

Looks like we are also moving the entire finder and resource system into moderngl_window. This will greatly reduce the size of this project but at least make it available through a library and not a framework (increasing the availability).

We still need to keep finder classes for effect directories etc.

[einarf]

moderngl_window is now on PyPI : https://pypi.org/project/moderngl-window/

Once the initial bugs/tweaks are committed + docs are published it should not take too long to integrate moderngl_window. It basically means merging conf and remove A LOT of code.