Better designs for email notifications

[excid3]

We don't currently have hardly any CSS for styling the email notifications. Even a basic template would work wonders here.

[excid3]

This would be an easy PR if someone is interested in making some contributions to open source.

[anquinn]

I could take a stab at it, but personally I like straight forward plain text, or very close to plain text notifications.

GitHub ones are super simple.

[excid3]

👍 I'm good with that.

For reference later on, Github email notifications look like this: