PURPOSE

Improve event mail scheduled communications: add a state and a contacted
count. Improve performances and code readability.

SPECIFICATIONS: STATE

Instead of the checkbox "sent", an event mail can have 3 values

  1. Sent, if all the mails has been sent;
  2. Scheduled, if scheduled but no attendee have been contacted;
  3. Running, if not all attendees have been contacted;

Note that communication targeting "after registration" are always considered
as being "running" as any new registration triggers a new communication.
A new widget is added that displays an icon depending on the state.
A new field holding contact count is added. When scheduler send emails it is
updated to keep a count of sent communications.

SPECIFICATIONS: MAIL COMPUTATION IMPROVEMENT

Purpose of this merge is to remove the "done" field computation. Indeed
it is based on either

  * mail_sent field if scheduler is global to the event (before or after
    event). This computation is light as this field changes only once
    when emails are scheduled and sent;
  * status of event registrations compared to all sent communication on
    those registrations. This is costly as adding a new registration changes

In this merge we therefore

  * rename ``done`` to ``mail_done`` to ease grep and understanding;
  * remove ``mail_sent`` as it is integrated within ``done``;
  * manually update ``mail_done`` when updating schedulers instead of doing
    it through a compute method;

Some code cleaning is performed to make it clearer and easier to understand.

LINKS

Task ID-2414658
COM PR odoo/odoo#63093
UPG PR odoo/upgrade#2014