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.

For the Content Report, I'm grabbing the siteUpdater after form submission in the js and showing it in an info box at the top.
For the Technical Report, same thing except that the email address is normally got in Java after the submission so I'm using the same logic 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.
This is static setup rather than something that should be run each time.