Count subscribed emails

It is a useful information to know how many subscription for a list.

assigned to @ced

added marketing type::feature + 1 deleted label

added 1 deleted label and removed 1 deleted label

New review356411002 at https://codereview.tryton.org/356411002/#ps354981134

New changeset 1e7bdc58c4a8 by Cédric Krier in branch 'default':
Count subscribed emails per list
https://hg.tryton.org/modules/marketing_email/rev/1e7bdc58c4a8

added 1 deleted label and removed 1 deleted label

closed

New changeset 24717bf3b3dd by Cédric Krier in branch 'default':
Count subscribed emails per list
https://hg.tryton.org/tryton-env/rev/24717bf3b3dd