Mass mailing restrictions

• Remove mass mailing user permission from all roles except from platform admin
• Restrict menu root visibility for mass_mailing users

Fixes: https://trello.com/c/HZDdW5I9/385-desactivar-acc%C3%A9s-al-m%C3%B2dul-de-massmailing-per-qualsevol-role-diferent-de-platformadmin