Enable declaration of the metadata's access-control

[AlasdairGray]

Each record should be able to declare who should be granted permission to view the record.

Extend the exchange metadata model to enable the declaration of the groups/roles who can view the record. The current distinction based on the accessRights value of OPEN, COMMERCIAL, or INTERNAL is not granular enough.

Research needs to be conducted in order to capture the appropriate access control levels that are required.