Markup and variable cleanup for titles and attributes in all templates

In the node template, we want the node title to be output as follows:

  {{ title.prefix }}
  {% if not page %}
    <h2{{ title.attributes }}><a href="{{ url }}" rel="bookmark">{{ title.label }}</a></h2>
  {% endif %}
  {{ title.suffix }}

But changing the title prefix and suffix should be done globally, and will affect many other templates as well, thus this separate issue.