spatialReferenceSystem rule change

[stansmith907]

Schema rules for spatialReferenceSystem:

Add elements:

• referenceSystemWKT (string) - "Well Known Text (WKT) for spatial reference system."
• referenceSystemParameterSet (object type: referenceSystemParameterSet) - "a complete parameter set of the projection that was used for the data set." See issue referenceSystemParameterSet new object #156.

Rules:

• any of [ referenceSystemType | referenceSystemIdentifier | referenceSystemWKT | referenceSystemParameterSet ]

mdJson:

   "spatialReferenceSystem": [
      {
         "referenceSystemType": "MD_ReferenceSystemTypeCode",
         "referenceSystemIdentifier": {},
         "referenceSystemWKT": "",
         "referenceSystemParameterSet": {}
      }
   ]

FGDC mapping:

<metadata>
  <spref>
      ...
  </spref>
</metadata>

ISO 19115-2 mapping:
The systemParameterSet maps to multiple classes in ISO 19115-2. These will be defined in lower levels of the schema definition.

ISO 19115-3 mapping:
Does not map to ISO 19115-1/3. This information was removed to ISO 19111.