domain rule change

[stansmith907]

New element for domain:

• "domainReference* {citation}: "reference to a standard or list which contains the members of an established set of valid values"

Rules:

• domainReference optional
• domainItem no longer required. Type of domain is determined as follows:

• description only = unrepresenatable domain
• description + domainReference = codeSpace domain
• description + domainItem = enumerated domain

mdJson:

{
   "domain": [
      {
         "domainId": "",
         "commonName": "",
         "codeName": "",
         "description": "",
         "domainReference": {},
         "domainItem": []
      }
   ]
}

ISO 19110-2 mapping:
The domainReference will be placed in an entity attribute section (carrierOfCharacteristics) as follows:

<gfc:listedValue>
  <gfc:FC_ListedValue>
    <gfc:label>
      <gco:CharacterString>external domain reference</gco:CharacterString>
    </gfc:label>
    <gfc:definitionReference>
      <gfc:FC_DefinitionReference>
        <gfc:definitionSource>
          <gfc:FC_DefinitionSource>
            <gfc:source>
              <gmd:CI_Citation>
                <gmd:title>title</gmd:title>
                <gmd:date></gmd:date>
              </gmd:CI_Citation>
            </gfc:source>
          </gfc:FC_DefinitionSource>
        </gfc:definitionSource>
      </gfc:FC_DefinitionReference>
    </gfc:definitionReference>
  </gfc:FC_ListedValue>
</gfc:listedValue>