Fix reference to non-existent upgrade profile introduced in f69e83c.

(Also removed an unused import).
Choose a different mail header date, since 1970... is default for DateTime and datetime (test results are nearly useless).
Add IDocumentMetadata behavior to ftw.mail.mail
Initialize metadata on mail.
Fill document_author metadata with fullname queried by email address (ogds).
Upgrade step: initialize metadata on extisting mail instances
Init missing field values in existing mails. Test metadata upgrade step.
Set delivery date on mail-out.
Use default value adapters to fill metadata on mail.
Fix Zope DateTime to python datetime conversion (timezone problem)
Remove specific mail index methods (document_date, document_author, receipt_date, sortable_author).
Move title and message into the common fieldset / Move title at first position.
Revert "Use default value adapters to fill metadata on mail."

This reverts commit d6b4718dbd272d0d28581bbaded8920aa06d9a60.

Conflicts:
	opengever/mail/mail.py
	opengever/mail/tests/test_mail_metadata.py