XX-11175: Expose REST API for Registration management

- api/registrations GET to retrieve all registrations in system. Query param start and limit to paginate
- api/registrations/user/{userId} GET to retrieve registrations for user based on internal id or username / alias. Query param start and limit to paginate. DELETE to drop registrations for user
- api/registrations/serialNo/{serialId} GET to retrieve registrations for mac address. DELETE to drop registrations for mac address
- api/registrations/ip/{ip} GET to retrieve registrations for given id. DELETE to drop registrations for ip
- api/registrations/callId/{callId} GET to retrieve registrations for call id. DELETE to drop registrations for call id
- api/registrations/server/{serverId} GET to retrieve registrations for server based on internal id or FQDN. DELETE to drop registrations for server

Exposed new query / delete functionality in RegistrationContext and junits. Deprecated methods that returns mongo cursor, will remove them in next version