Add Sevenoaks responder as invalid reply address
Add Sevenoaks responder as invalid reply address

This commit adds `autoresponder@sevenoaks.gov.uk` as an invalid reply 
address meaning users will not be able to send follow-ups or internal 
review requests to it. Linked to #670

mysociety/whatdotheyknow-theme,mysociety/whatdotheyknow-theme,mysociety/whatdotheyknow-theme