Revert "mapistore: Bypass Embedded message creation for Tasks in Outlook"

This reverts commit a82625ee40bef7fc7fa663e56c0ff10553974e42.

Initial commit was totally wrong and it is the backend that
needs to handle 'not-implemented' conditions gracefully.
Merge pull request #34 from Zentyal/kamenim/revert-sogo-backend-bypass

Revert "mapistore: Bypass Embedded message creation for Tasks in Outlook