Support STARTTLS when sending email notifications

TriggerActionMail only supports SSL connections where the mail server automatically starts SSL immediately when a connection is established. It would be good to also support starting encryption using the STARTTLS command.

This can be done by setting the property "mail.smtp.starttls.enable" to "true" when creating the mail session object.

The usual ports for email are:

• 25 - Clear text or optional STARTTLS
• 465 - SSL
• 587 - Clear text or optional STARTTLS

At the same time it would be good to check whether we support encryption without authentication (if we don't, then we should fix that).