Feed item email should include more metadata

[elliotf]

A feed item email should include more metadata:

• author (because the from field is the feed source)

Metadata that should not be included:

• date published -- while gmail uses the delivery date in the message list, the Date header is shown in the message view

[elliotf]

It would probably be a good idea to use a template rather than ad-hoc string concatenation, too.