Module rewrite + GUI

[ghost]

This commit features a few things:

• A GUI that everyone has been looking forward to
• Rewritten into a module with a Class so the installer can be used in your own scripts
• Readme has a few changes

Image of the GUI:

(TKinter looks ugly on Linux, curious to see how it looks on Windows/MacOS)

Might need some testing but works nonetheless

[ihaveamac]

Thanks, I'll give it a try soon.

[ihaveamac]

Windows 10, version 1903

macOS 10.15.1

Note that due to pyinstaller/pyinstaller#4334 the tkinter gui most likely won't work from a standalone version on 10.14.6. 10.14.5 or earlier, and 10.15.0 or later seem to work fine.

[ihaveamac]

I'm going to manually pull this into a different branch to leave master untouched until a full release is ready.

[ihaveamac]

https://github.com/ihaveamac/custom-install/tree/module-rewrite

Thanks!