GET /knowledge-graph/datasets/:id to return info about visibility

[jachro]

As a renku-graph API user, I'd like the Dataset Details resource (GET /knowledge-graph/datasets/:id) to return info about the DS visibility.

Acceptance criteria:

• visibility property to be added to the response payload of the GET /knowledge-graph/datasets/:id;

  ...
  "created": "2012-10-15T03:02:25.639Z", 
  "project":  {
    ...
    "path": "namespace1/project1-name",
    "visibility": "private"
  },
  ...

• the value of the property to be visibility of the Project where:
  • the DS was created on first;
  • the DS is still active on it;
  • the DS has no modifications on it;