[IMP] mail: first implementation of tracking and bounce management.
Added 2 fields on mail_mail to count read/bounce.
Added bounce alias bounce-mail_id-model-res_id.
Added message_receive_bounce method that try to incremetn message_bounce field.
[FIX] mail_mail: fixed reply_to computation (before create was leading to a wrong message_id to the embedded mail_message); mail_thread; fixed private discussion not going through the route checking; improved replying through mailgateway now incrementing the replied field of mail_mail.
[ADD] mass_mailing: added module for mass mailign campaigns. First draft of new module :
simple mass mailing campaign model, linked to emails, compute some statistics
mail.compose.message updated to the mass mailing campaigns in mass mail mode
[MERGE] Sync with trunk
[MERGE] Sync with trunk
[FIX] crm: fixed a bug introduced when merging trunk
[IMP] mail_mail, mail_message: various improvements to try to improve message creation time
Replaced some read by browse
Moved get_reply_to from mail_mail to mail_message
Hint: specifying email_from, reply_to help to enhance computation time

[REF] mail: cleaned some tests, renamed a file, moved mail_group tests into a dedicated file
[MERGE] Sync with trunk
[REF] mail_followers: cleaned notify methods, lessening the number of queries.
[FIX] crm: fixed regression in merge_notify, due to a cleaning in opportunities merging a few months ago
[FIX] mail_message: fixed reply_to and email_from computation in create: take also False values, only undefined values trigger the default one
[IMP] mail.compose.message, email.template: rendering is now done in batch.

Also refactored send_mail in mail.compose.message in order to be able to override
mail values without having to intefere with the send_mail behavior.
[IMP] mail_message: cleaned search view
[MERGE] Sync with trunk
[IMP] mass_mailing: added kanban views for mass_mailing, implemented segment for campaigns. Moved sparkline and gauge widgets to web.

Segment: template, date, mails.
Campaign: grouped statistics.
[FIX] mass_mailing, crm: fixed sparkline options
[IMP] mass_mailing: added fields on segment form view + rules for segment model
[MERGE] Syn with trunk
[IMP] crm, mass_mailing, sale_crm: added dependencies to web_kanban_gauge/sparkline newly introduced modules
[ADD] mass_mailing: added directories + skeletons for doc and tests