[IMP] mail.compose.message: now proposes to work on active_domain
[IMP] mail: mail.message now has mail_server_id from template_id.
[IMP] mail: better implementation of active domain / use active domain
[MERGE] Sync with trunk
[MERGE] Sync with trunk
[FIX] mail_compose_message: keep empty domains
[IMP] mail_compose_message: pass new fields as invisible before merging
[TEST] mail: added test for support of active_domain
[DOC] mail, email_template: added changelog
[MERGE] [IMP] mass mailing improvements: use active_domain from list view, better management of templates

mail.message: now have mail_server_id field, taken from mail_mail, to be able to store preferences about the server to use to send notification emails

email.template: mail.compose.message:
- now handles mail_server_id from the template
- improved user_signature management from templates

mail.compose.message: now can use the active_domain form context, taken from the list view. This means that when checking all records through the header hook, the mass mailing is done on all the records that match the search domain, not only to the ones in the displayed pager.
[FIX] mrp_operations: undefined name.