This removes some code which is duplicative and obscure (ie it’s not
very clear why we do `"a" * 73` even though there is a Very Good Reason
for doing so).
* Added a new method to the ComplaintApiClient to get the total
complaints by date range from the API.
* Added a new method to the ServiceAPIClient to get the new platform
admin stats data from the API.
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.