get_atomic_template() should not load once.  Allow it to load a template multiple times.
Introduce the template.php file and the hybrid_get_content_template() function.
Deprecate get_atomic_template().  Atomic templates will be revisited in the next major version of the framework.
Use the default setting if it has not yet been set via the theme settings page.  This is particularly useful if a theme adds new settings in an update.