Initial handling for edits on encrypted drafts

* src/mail.cpp (Mail::updateOOMData_o): Cache body for
drafts, too.
* src/mailitem-events.cpp (Write): Encrypt drafts again on write.
(Close): Let Outlook ask for "want to save changes" for drafts.

This is still extremly buggy. Somehow after the write
in which we prepare the encrypt MAPI is not updated.
So we have to take our information from OOM. That's never
good.