[mass_mailing_distribution_list]
[ADD] Add a controller to manage unsubscribe url
[ADD] tests to cover new features
[ADD] mail_mail: customize unsubscribe url case of newsletter
[CHG] distribution_list: update_opt in/out to update the m2m list
[CHG] mass_mailing: allow to manage returned text for unsubscribe url
[FIX] distribution_list: opt in and out are m2m