[Reviewer: Alex] Sto755

Alex, can you please review these changes for sto755?

They cover:
 - Accepting emergency registrations without authentication
 - Storing whether a registration is an emergency one in the RegStore
 - Preventing user-initiated deregistrations of emergency registrations
 - Adding a config option to Bono to control whether it accepts emergency registrations
 - Subscriptions/Notification/Application server changes

Still to come are the changes to prevent network-initiated deregistration of emergency registrations, and live test updates. 

(Also fixes #508)