[tor-browser-en] pass through unknown args to firefox
[tor-browser-en] take long argument names

--help and --update
[tor-browser-en] actually support alternate directory

using --dir= and not -r, which never worked!
[tor-browser-en] attribution
[tor-browser-en] document the new arg passthrough feature
[tor-browser-en] separate GNOME app group

suggested by computerwhiz1 in comments
reported here https://trac.torproject.org/projects/tor/ticket/11102
can revert if/when upstream fixes it
[tor-browser-en] arguments with spaces are broken