Issue #2668420 by bryanbraun: fix extra padding and non-date centering.
The extra padding was due to a CSS specificity error, but I also noticed
that the padding wasn't adjusting when the content-type chooses not to
display the publish date. That fix was included because it affects page
padding as well.
Issue #2575581 by bryanbraun: Update APIs to use several new Drupal 8 paradigms.
- Move default theme settings to config/install/writer.settings.yml
(see also https://www.drupal.org/node/2382645)
- Change the check_plain reference to Html::escape (see also
- Change code-snippet CSS files into libraries (see also