cancel as AJAX call and new tooltips in buildview

 * Calling to 'cancel' in the webUI is performed using AJAX now, which means no
   more reloading of the full list or the full overview (builview)
 * The rest of the scheduler calls will follow
 * The action's menu in buildview is now also rendered using AJAX, to react to
   the changes.
 * Changed the tooltip library from wz_tooltip to Opentip (which supports both
   prototype and jQuery).