Panels everywhere for Drupal 8. Takes over the page.html.twig and places layout configurations in layouts.
Panels - https://www.drupal.org/project/panels Page Manager - https://www.drupal.org/project/page_manager Layout Plugin - https://www.drupal.org/project/layout_plugin Ctools - https://www.drupal.org/project/ctools
Visit /admin/modules and install Panels Everywhere through the ui. This will turn on required modules.
Turning on "Page Manager UI" module will allow users to see the new site template.
After the module is enabled, a new page will show on the page manager edit page that is disabled. /admin/structure/page_manager
Users can now edit that page and add "Main Page Content" to the layout, as well as other pieces of the site required for the site's page template.
So far the site template gets taken over and elements can be moved to different regions through the dropdown in page manager. This is a work in progress so there will be bugs!