update how CUI are handled to better assist in new DataStore CUI designations

[RobLBaker]

-keep CUI in additonalMetadata
-allow only 1 of 1-32 different codes for designating the legal authority for restricting data (or make it public)
-use API lookup for list of codes and to extract code-related information
-generate and display CUI:

PUBLIC:

<additionalMetadata id="CUI">
     <metadata>
          <distribution>
               <CUI>PUBLIC</CUI>
          </distribution>
     </metadata>
</additionalMetadata>

RESTRICTED:

<additionalMetadata id="CUI">
    <metadata>
         <distribution>
             <CUI>RESTRICTED</CUI>
             <authorityDesignator>Robert Baker</authorityDesignator>
             <contactEmail>robert_baker@nps.gov</contactEmail>
             <description>This material contains information concerning the nature and specific location of a National Park System resource that is endangered, threatened, rare, or commercially valuable, of mineral or paleontological objects within System units, or of objects of cultural patrimony within System units.</description>
             <label>National Park System Resources</label>
             <marking>CUI//SP-NPSR</marking>
             <onlineUrl>https://www.archives.gov/cui/registry/category-detail/national-park-system-resources#authority-list</onlineUrl>
             <type>CUI</type>
          </distribution>
     </metadata>
</additionalMetadata>