Set debian policy to 3.9.6
Set debhelper deps to 9.0
debian/pantheon.desktop:
debian/pantheon-session:
  - Add wrapper for launch pantheon session sincce debian Xsession does
    not support parameter to gnome-session
debian/pantheon.session:
  - Set gnome has fallback session.
  - Force XDG_CURRENT_DESKTOP on Pantheon.