Replace the inlined header.article-meta with call to a partial, and fix rendering when empty

[chalin]

The element <header class="article-meta"> is inlined in several layouts, with the same content I believe (and will double check):

layouts/_default/content.html:
  4: 	<header class="article-meta">
  5  		{{ partial "taxonomy_terms_article_wrapper.html" . -}}

layouts/_default/taxonomy.html:
  20:           <header class="article-meta">
  21              {{ partial "taxonomy_terms_article_wrapper.html" . -}}

layouts/blog/content.html:
  8: 	<header class="article-meta">
  9  		{{ partial "taxonomy_terms_article_wrapper.html" . -}}

layouts/blog/list.html:
  22:         <header class="article-meta">
  23            {{- partial "taxonomy_terms_article_wrapper.html" . -}}

layouts/docs/list.html:
  5: 	<header class="article-meta">
  6  		{{ partial "taxonomy_terms_article_wrapper.html" . -}}

layouts/swagger/list.html:
  5: 	<header class="article-meta">
  6  		{{ partial "taxonomy_terms_article_wrapper.html" . -}}

IMHO, there are formatting issues the result from that header element being included in pages while still being empty. It would be best to fix this after refactoring the layouts to use a single partial.