Ability to set wayland environment variable in launcher

It'd be nice to have checkbox for setting MOZ_ENABLE_WAYLAND=1 through click of a button in launcher. Tails uses Wayland (no idea why not enabled in Tor by default) so it'd be cool to have as an option in launcher instead of having to manually set it.

Copy of issue on github: https://github.com/torproject/torbrowser-launcher/issues/744