[MERGE] mail, various: update record when creating a customer from chatter suggestion

Currently using chatter it is possible to create customers directly when
posting a message. Unknown email addresses are proposed to the user that
can create customers directly in the posting process.

However the record is not updated. Several models like lead, issue, ticket
or event track have a customer (partner_id) field that is not updated even
when a customer is created from the chatter. Users have to update records
manually.

This merge automates it by updating the record through a post process
hook on message_post that is used in main customer-based addons. A small
improvement is done in the chatter to reload the record once posting a
message to a new customer.