[FIX] mail: backport of saas-2 revision 9065 and 9081.

Make sure the user is subscribed before the super() call in mail_thread. This allows to have follower based record rules working (eg: note.note)
[IMP] mail: check at least access_rights in case of creation
[IMP] mail: in case of creation, still check creation access rights for subscription
[MERGE] [FIX] mail: mail: backport of saas-2 revision 9065 and 9081 and security improvements.

Add followers before super call in mail_thread creation.
This allows to have a value for the _set_followers call and be able to have record rules based on followers at creation.

Set the priority of message_follower_ids fields to -10 (default is 0) to be sure it will be executed before other function fields using these followers (eg: _set_stage_per_user from note.note does a browse which would trigger record rules to read the note)

Context hack to avoid checking read access at creation of the record (check create rules instead)
[ADD] stock: update pot file to latest version of translations
[FIX] point_of_sale: validate and closing pos sessoin handle multi company

When the user who validated and closed the pos session was not the same user who created the session, and if this user was not in the same company, it wasnt possible to validate and close the pos session.

This explanation if also valid if the user who created the pos session changed of company in his preferences between the creation and the validation.