Provide an IntIdResolver adpater to generate Dossier Mail-In addresses

based on IntIds, and use it instead of the old implementation.
Removed og.mail IMailSettings registry interface (now done in ftw.mail).

Added upgrade step to migrate settings to ftw.mail's IMailSettings and
remove old og.mail IMailSettings.
Hide standard ftw.mail mail-in viewlet (we display the mail address in the byline).
Update mail related tests.

- Mails can't be added inside tasks. Neither directly nor via mail-in.
- Expected mail domain should be set in test itself
Use ftw.mail from source until we create a KGS that uses >= 2.0.