they're currently expecting a RecipientsCSV object - but we won't
always have that available if we're handling a single notification.
So make the partials take generic variables, and then use a jinja with
block to pass in the correct values from either the check csv page or
the check notification page.
Additionally set the notification check page to show errors nicely -
hide the send button if there were problems, and replace the header
rather than creating a job, after entering the placeholders, you now
send a single notification. This means we don't clog up s3 by creating
lots of one line CSV files.
