A platform admin form accepts a list of references (one per line)
received from DVLA and sends them to the API to update notification
statuses.
References we get from DVLA start with `NOTIFY00\d`, which isn't
part of the reference we store in the database, so we remove them
before sending the data to the API.
The new `returned-letter` status should be treated as `delivered`
for now until we decide a way to display returned letters to users.
A new platform admin page Email complaints has been added to surface those complaints.
Eventually the complaints will be visible to the services so they can remove the email address from their mailing list.
Next thing to implement is "x email complaints" warning on the platform admin summary page.
There are way too many links in the top nav now (when you’re using the
site as a platform admin).
And how often are you going to look at the letter jobs page really?
This commit adds some internal navigation for the platform admin area of
the platform, copying the style that works for navigating a single
service.
