add cross-db transaction support 1.2.0

You can do cross-db transactions now:
```php
 $manager = new \Phalcon\Mvc\Model\Transaction\Manager();

 $manager->setDbService("vs_hotel");
 $tran1 = $manager->get();

 $manager->setDbService("vs_common");
 $tran2 = $manager->get();

 $pointModel = new PointModel();
 $pointModel->setTransaction($tran2);
 $pointModel->name = "ttt";
 $pointModel->position = "[122, 3432]";
 $pointModel->city_id = 323;
 $pointModel->city_py = "hello";

 if($pointModel->save() == false) {
     foreach($pointModel->getMessages() as $message) {
         echo $message->__toString() . PHP_EOL;
     }
     $manager->rollback();
 }

 $eqsModel = new EQSModel();
 $eqsModel->setTransaction($tran1);
 $eqsModel->out_id = "343";
 $eqsModel->entity_id = 3343;
 $eqsModel->vendors = "[fdfd]";

 if($eqsModel->save() == false) {
     foreach($eqsModel->getMessages() as $message) {
         echo $message->__toString() . PHP_EOL;
     }
     echo "=====---eqs rollback---======\n";
     $manager->rollback();
 }
$manager->commit();
```