Add gmail instructions for submission.torproject.org

See merge request tpo/tpa/wiki-replica!21

Hi!  Please merge this only if you think it will be helpful, and
feel free to clean it up or edit it any way you want.

Turns out that we don't use the `postgresql` module at all right now,
and `dip::database` has been removed. We have an Installation section now.

The vast majority of our users will *not* use msmtp and might be
confused by this, especially in the tutorial. Bury it a little deeper
in the how-to section, which I'll add to in a minute.

This procedure was just tested live with status.torproject.org by
@lavamind.

Also, the daemon is configured to start automatically so there should be
no need to launch it manually.

Also adds a fix for schleuder-cli config