admin: add email alerts, and maybe SMS too

[buck54321]

As system monitoring is added (see #1322), it would be great if there were configuration options to send an email to an administrator when the system state goes downhill. This would require credentials for an SMTP server, but I think most email services have those creds available if you know where to look.

Additionally, SMS alerts could be enabled via Twilio, though some may understandably object to the use of a commercial product.