SerializeJob should add get_class() as metadata name to the job instance being serialized.

Simple tests will fail as a created job instances are not equal to the one that is pushed and then pop'd/peek'd
```
    public function testPeek()
    {
        $job = new SimpleJob();
        $this->queue->push($job);

        $peekedJob = $this->queue->peek($job->getId());

        $this->assertEquals($job, $peekedJob);
    }

1) SlmQueueDoctrineTest\Queue\DoctrineQueueTest::testPeek
Failed asserting that two objects are equal.
--- Expected
+++ Actual
@@ @@
 SlmQueueDoctrineTest\Asset\SimpleJob Object (
     'content' => null
     'metadata' => Array (
         'id' => '1'
+        'name' => 'SlmQueueDoctrineTest\Asset\SimpleJob'
     )
 )
```