Create mail-sending submodules

[callahad]

Though we only need raw SMTP support to launch, we'll may want to be able to switch between various delivery strategies in the future: console logging (testing), raw SMTP, specialized APIs like Amazon SES, SendGrid, etc.

We should:

• Define an interface that delivery strategies must implement
• Implement a console logging strategy that does not actually send mail
• Implement a strategy that uses SMTP to send messages
• Allow strategies to be selected via a configuration file