Allow admins to send news items as news letters

[kirahowe]

Allow admins to create news letters, that can include many news items as well as a custom message at the top, and then send them via email through a UI.

Maybe piggyback on admin email sending. Just add the ability to add news items to existing group emails.

• create news letter resource
• news letter creation includes selecting which news items are included in it and writing a custom message
• allow admin to select users to send the newsletter to
• keep a log in the UI of what was sent to who