WL-3566 : Add email sent confirmation message to feedback tool

This is only for logged in users. WL-3576 is for non logged in users.

I'm grabbing the siteUpdaters after form submission in the js and showing it in an info box at the top.

For the technical toAddress, same thing except that the email address is normally got in Java after the submission so I'm using the same one-liner to put it in the request before, before getting it out again in the js afterwards.

I'm re-using as much of the css for the error message as possible.