Currently there is confusion between responsibilities of
metainfo.Endpoint, metainfo.Service, PointerDB.
By separating database "service" into a separate package and
its types allows to disentagle them.
This gives us responsibilities:
1. metainfo.Endpoint - translates requests and permissions
2. metainfo.Service - handles requests and coordinates with
objectdeletion, piecedeletion, metabase
3. metabase.Service - communication with the database interface and invariants
Currently metabase will contain the types necessary to coordinate
information.
Change-Id: If8c992b4b9d9e70a56bbd8a378a5af6b1a2ec34e
