Scratch 3.0 Dark Theme Userscript (and general theme framework)

Some work is still needed, but it is pretty much done.

I use the Tampermonkey extension for userscripts. Get it at https://tampermonkey.net/. Install userscript from here: https://github.com/infinitytec/3.Dark/raw/master/3dark.user.js

I included notes so you should be able to find your way around. Note that this falls under the MIT License, which I found appropriate.