[IMP] share: better way to restrict the feature to the technical group.

Reverted commit 57a12121057df9fee039a54f5b947c0e8a917fe9 that introduced an unnecessary
call to has_group, as it could be done un share_wizard.py once for the session.

Removed the group_share_user, not necessary anymore.
[IMP] base: Display title in contact modal form

As a contact-specific information, it would be nice to display the title in the contact modal form.