B"H web: add checkbox to choose to mute Esc key beep sound

First of all, thanks for doing this project! It is an awesome idea!

Second of all, I usually disable audio on the terminal, so here's a patch to do the same here. :-D

Feel free to change; this is just a mockup and example so you don't have to do the work.

P.S. This pull request was done thru the web interface; the functionality was,  however, tested, using the Firefox dev tools javascript console (and another "data:text/html," page).