[FIX] mail: various fixes
Mass mailing: emails due to mass mailing are not queued instead of sent immediately.
As most of cases go through mail_followers._notify(), a new argument is added that
allows to control the force_send (like what is done in email_template).
Chatter: better display of recipients when having a message_post due to mass mailing
(not always displaying logged a note).
Notified people: when having no subtype, just avoid notifying the followers but
take into account specified recipients (partner_ids).
[FIX] [IMP] mail: allow to use message_post on models not having message_post method defined.
mail.compose.message wizard and messaage_process now check that the active model
has message_post defined. Otherwise using thread_model context key that is better
managed in message_post, it is possible to use mail_thread.message_post() with a
thread_model and thread_id that should not allow message_post otherwise.

Hint: look for backport into 7.0
[FIX] email_template: allow to define context action even without having create access on ir.values and ir.action

Hint: look for backport into 7.0
[FIX] mail.compose.message: supports user_signature of template. Note that in case of multiple wizards (send on ids that is not a singleton list), user_signature on one template is valid for all wizard.
[FIX] mail.compose.message in email_template: var typo
[FIX] mail_mail: sdearch view: no need to have default_type_email
[FIX] mail.compose.message: fixed reply_to from template in mass mailing.
[FIX] mail_mail: reply_to: use tools.email_split to avoid issues when handling email addresses.
[IMP] mail_message: added reply_to to the form view of mail.message
[IMP] mail: mass_mailing: avoid having 'Followers of' when having a specified reply_to coming from the mail_message
[CLEAN] mail: cleaned reply_to code, finally.
[TESTS] mail: added tests
[MERGE] [FIX] mail, email_template: various fixes
- [FIX] [IMP] mail_thread: allow to use message_post on models not having message_post method defined. mail_compose_message.send() wizard and mail_thread.message_process() now check that the active model has message_post defined. Otherwise using thread_model context key, it is possible to use mail_thread.message_post() while keeping model and res_id on the created mail_message.
- [FIX] [TESTS] mail_message, mail_mail: fixed reply_to and email_from default / specified values + added tests (mostly backported from trunk)
- [IMP] mail_message, mail_followers: _notify now have 2 new arguments force_send and user_signature. force_send allows to immediately send the notification emails. user_signature tells whether to add the author's signature in the notification emails sent.
- [FIX] mail_message: notified people: when having no subtype, just avoid notifying the followers but take into account specified recipients (partner_ids).
- [FIX] mail_mail: removed duplicate field email_from, as it is already defined on mail_message (mail_mail inherits from mail_message).
- [IMP] mail_mail: no need to search on type = email in list view.
- [FIX] email_template: allow to add a context action even without having create access on ir.values and ir.action by using SUPERUSER_ID.
- [FIX] mail_compose_message: support user_signature of template. Note that in case of multiple wizards (having ids), user_signature=False on one template is used for all wizards.
- [FIX] mass mailing: emails due to mass mailing are not queued instead of sent immediately.
- [IMP] Chatter: better display of recipients when having a message_post due to mass mailing (not always displaying logged a note).