Work for #426 - should help fix problems with encoding when sending messages in the, "Send a Message" screen, and "Send an Invitation" screen. 

No changes in behavior will be seen in the, "Send a Webpage" screen, as messages are constructed using MIME::Lite::HTML. I think the underlying problem is with using MIME::Lite - it doesn't look like it's marked as being worked on, and the current maintainer notes getting weird bugs that they're not going to fix, but states alternatives. One of them, MIME::Entity, is the one we're using, as it's already used in other places in the app.
This make list invites work, again.
Let's see that Invite button!
Little change in the email template
Let's let 'em know if a field is required!