Disable GitHub Shortcuts από hayatogh

This add-on disables ALL GitHub keyboard shortcuts.
When the URL starts with https://github.com or its subdomains, keyboard shortcuts like "Ctrl-B" are ignored on GitHub web and delivered to Firefox.

In the case of "Ctrl-B", which expands/collapses file tree on code view, it is ignored and delivered to Firefox to open/close Firefox Bookmark Side bar.

This add-on blindly disables all keyboard shortcuts;
after the installation of this add-on, "Ctrl-B" in text boxes will not surround words with "**" to make it bold.
And the GitHub web editor will also not work.

Currently, I have no plans to implement features like allow-listing some keys or changing behavior based on what is focused but any comments are welcome :) I'm not so familiar with GitHub workloads on the web interface, maybe there are some useful shortcuts worth implementing them.