email: Always include a message-id token

Previously, if the quoted response mechanism was disabled, then outgoing mail would also not include the message-id token. This breaks the correlation of email to ticket-thread. Now, the message-id token is always embedded in HTML emails even if the quoted-response removal system is disabled.

(Turns out that the message-id token was always included in text bodies.)

*This patch also omits the reply-tag on system log alerts*