added USB camera preview window. still needs right aspect ratio/ui fixes

[jullrich]

[may not be ready to be pushed to the "main" branch, but pushing it for testing]

This is the first (working?) attempt to include a preview window with a live webcam feed. Note that the browser will only access the camera if the file is loaded from a web server. Loading as a file will not work. The simplest way to set up a web server is Python. Just run

python3 -m http.server --bind 127.0.0.1 9000

in the same directory as index.html

This will start a web server on localhost port 9000.

Access the page using:

http://localhost:9000/

Select the webcam for the dropdown. This will require some form of HDMI->USB interface.

Issues remaining: mostly UI. For example, the video window size must be adjusted according to the camera requirements not to distort the aspect ratio.