Add support for page template

I've added the following to the bottom of zuvi.theme, it allows using page templates per content type.

/**
 * Implements hook_theme_suggestions_page_alter().
 */
function zuvi_theme_suggestions_page_alter(array &$suggestions, array $variables) {
  if ($node = \Drupal::routeMatch()->getParameter('node')) {
    $suggestions[] = 'page__' . $node->bundle();
  }
}