[MERGE] OpenChatter "Invite Yur Mummy" Invite branch
Featuring :
- Invite wizard, to add followers to a document, and to send them an email
- Invite button in Chatter, that calls the Invite wizard
- each send notification is a distinct email, one for each partner to have to receive a notification. Changes in mail_followers and mail_mail to handle this. If send receives a notifier_ids parameter, it uses it instead of the mail_mail.email_to field, and send an email to each partner. Overriding some of the methods allow to somewhat personnalize the email
- Portal: add the signin url in notifications send to portal users
- Tests: made a class for tests using emails, defining and removing mockups for the gateway. Updated mail tests, added an invite test in portal.