Youtube Empowered wót Magnus Anderson

Motivation:
The 'Enhancer for Youtube' extension is very useful and powerful, which is why it is all the more tragic that it is proprietary. So, I want to implement all the features (that I think are useful) from that extension in libre code.

Repository: https://github.com/magnus-ISU/youtube-empowered

List of features:
- Videos start in theater mode by default
- Videos in Theater mode take up the entire viewport
- Scrolling down beyond the video playback area shows a mini player that follows you

List of planned features from Enhancer:
- Prevent autoplay on videos in the background

List of planned features not from Enhancer:
- Keyboard navigation for comments, like RES
- Have a way to show only comments below a video, only the description, or only recommendations; like NewPipe

List of features that will not be added:
- Ad-blocker: Use uBlock Origin
- Speed controls: Use Video Speed Controller
- Theming: Install Stylus
- Cinema Mode: Use a dark theme