add minimal metadata for articles

[tcatapano]

using minimally valid elements with dummy data pending further specification and development

[tcatapano]

minimally valid markup added to xslt, e.g.,

note: we will seldom have values for the required journal-id and issn

<front>
      <journal-meta>
         <journal-id journal-id-type="other">N/A</journal-id>
         <journal-title-group>
            <journal-title>Science</journal-title>
         </journal-title-group>
         <issn>N/A</issn>
      </journal-meta>
      <article-meta>
         <title-group>
            <article-title>A lost world in Wallacea: Description of a montane archipelagic avifauna</article-title>
         </title-group>
         <pub-date date-type="pub">
            <day>10</day>
            <month>01</month>
            <year>2020</year>
         </pub-date>
      </article-meta>
   </front>