Drupal 7 — Default page template with panels

template.tpl.php

<?php

/**
 * Helper function to test for panel page config.
 */
function _is_panel_page() {
  $page = &drupal_static(__FUNCTION__);

  if (function_exists("page_manager_get_current_page")) {
    if (!isset($page)) {
      $page = page_manager_get_current_page();
    }
  }
  return $page ? $page : FALSE;
}


/**
 * Implements hook_preprocess_html().
 */
function HOOK_preprocess_html(&$vars, $hook) {
  if ($page = _is_panel_page()) {
    // Add a body class for panel pages.
    $class = 'page-panel';
  }
  else {
    // Add a body class for default pages.
    $class = 'page-default';
  }
  $vars['classes_array'][] = drupal_html_class($class);
}


/**
 * Implements hook_preprocess_page().
 */
function HOOK_preprocess_page(&$vars, $hook) {
  if ($page = _is_panel_page()) {
    // Add template suggestion for all panel pages.
    $vars['theme_hook_suggestions'][] = 'page__panel';
    // Add template suggestion per panel page.
    $vars['theme_hook_suggestions'][] = 'page__panel__' . $page['name'];
  }
}