Integrate user/group lookup/filter into Orthanc so that Orthanc is able to verify user identity when creating comments and ACL policies

The Sonador web application provides a set of "filter" endpoints that allows for retrieval of user and group details by introspection of tokens and UID. There are multiple endpoints in Orthanc which require the functionality in order to ensure that only authorized users are able to access, view, and edit comments and access control policies.

Development tasks:

• Add user and group lookup calls to ACL and comments GET methods, modify responses to return the detail payload for the user and group rather than only the UID (4f6820c7)
• Add user/group introspection calls to ACL and comment creation, ensure that the user/group UID exists and has access to the server
  • Call for user introspection at time of comment creation: 4f6820c7
  • Call for user introspection at time of user ACL policy creation: 4f6820c7
  • Call for group introspection at time of group ACL policy creation: 3cb29f02
  • Test case for group ACL validation: sonador-client@a2dfffe4