When saving and loading datasets, map metadata qualities to Dataset metadata

Once this is merged:

• https://gitlab.datadrivendiscovery.org/MIT-LL/d3m_data_supply/merge_requests/12

Then any additional metadata could be represented as a quality of the form:

"qualities": [
  {
    "qualName": "metadata",
    "qualValue": {
      "semantic_types": ["https://metadata.datadrivendiscovery.org/types/Attribute"]
    },
    "qualValueType": "dict",
    "restrictedTo": {
      "resID": "0",
      "resComponent": {
        "selector": ["__ALL_ELEMENTS__", 0]
      }
    }
  }
]

We should add code to the Dataset loader to load such metadata and merges it with other metadata.