#796 Contact us address display

[arnaudherve]

Admin should be able to deactivate the "Contact us by
e-mail" option. Obvious security and privacy reasons.

A special Admin page with all Contact Us options would
be handy. At the moment it is excessively scattered.

Admin should be clearly informed that his addresss is
displayed.

Maybe add a sort of form to make a special user for that
purpose.

Maybe add a default address info@site.site