Make mobile menu toggle text configurable

Description of the need

Right now the mobile menu toggle text is hardcoded (though translated) as Menu. Does it seem reasonable to folks to allow that text to be adjusted on a per menu block basis? (ie. when configuring the block, it defaults to Menu but can be overwritten)

      $data['content']['#prefix'] = theme('menu_toggle', array(
        'enabled' => $config['toggle'],
        'id' => $id,
        'text' => t('Menu'),
      ));

I am considering a case where there are potentially two toggles (in different parts of the page) and it would be helpful to be able to use different language for each. At first I thought I'd just override theme_menu_toggle but I really don't have enough information to grab onto inside that function to know much about the particulars of the menu.

If we add this, it could only appear underneath the "Display menu toggle..." option if it was selected: