Simplification of node.html.twig

As part of an initiative to clean up the markup in core, the following changes have been made to node.html.twig.

Summary

• Removed id="node-#" from <article>
• Updated user_picture variable to author_picture
• Added author attributes for RDF
• Made CSS follow the Layout rules in CSS architecture (for Drupal 8) - Separate Concerns
• Added classes in attributes.class:
  
  • .node
  • .node--$nodetype
  • .node--promoted
  • .node--sticky
  • .node--unpublished
  • .node--preview
• Removed submitted variable and replace with author_name and date variables
• Updated CSS for Bartik to match new classes

Default node template - core/modules/node/templates/node.html.twig

Before

<article id="node-{{ node.id }}" class="{{ attributes.class }} clearfix"{{ attributes|without('id', 'class') }}>

  {{ title_prefix }}
  {% if not page %}
    <h2{{ title_attributes }}>
      <a href="{{ node_url }}" rel="bookmark">{{ label }}</a>
    </h2>
  {% endif %}
  {{ title_suffix }}

  {% if display_submitted %}
    <footer>
      {{ user_picture }}
      <p class="submitted">{{ submitted }}</p>
    </footer>
  {% endif %}

  <div{{ content_attributes }}>
    {{ content|without('links') }}
  </div>

  {{ content.links }}

</article>

After

<article{{ attributes }}>

  {{ title_prefix }}
  {% if not page %}
    <h2{{ title_attributes }}>
      <a href="{{ url }}" rel="bookmark">{{ label }}</a>
    </h2>
  {% endif %}
  {{ title_suffix }}

  {% if display_submitted %}
    <footer class="node__meta">
      {{ author_picture }}
      <div class="node__submitted {{ author_attributes.class }}"{{ author_attributes|without('class') }}>
        {% trans %}Submitted by {{ author_name|passthrough }} on {{ date }}{% endtrans %}
        {{ metadata }}
      </div>
    </footer>
  {% endif %}

  <div class="node__content {{ content_attributes.class }}"{{ content_attributes|without('class') }}>
    {{ content|without('links') }}
  </div>

  {% if content.links %}
    <div class="node__links">
      {{ content.links }}
    </div>
  {% endif %}

</article>