Implement units loading in Zen mode

Signed-off-by: Michal Čihař <michal@cihar.com>
Initial Zen saving support

Signed-off-by: Michal Čihař <michal@cihar.com>
Log SMTP errors rather than failing the request

Signed-off-by: Michal Čihař <michal@cihar.com>
Merge branch 'master' into bootstrap