www-client/firefox-bin: use wrapper

www-client/firefox-bin: use wrapper

This change will replace /usr/bin/firefox-bin symlink with a
wrapper script:

- Using a wrapper will allow us to set additional variables
  more easily.

- The wrapper will address an issue that prevented external applications
  from opening links when a Firefox instance was already running.

- In general, the wrapper will allow user to execute 'firefox-bin' from
  wherever and whenever they like without getting an error that an
  instance is already running.

In addition, Wayland support was exposed via USE flag.

Package-Manager: Portage-2.3.96, Repoman-2.3.22
Signed-off-by: Thomas Deutschmann <whissi@gentoo.org>