Gearman service returns GearmanJobStatus from addJob

Gearman::addJob now returns a GearmanJobStatus object which contains the job handle and Gearman client return code associated with the task.

Example:
```
$jobStatus = $this->gearman->addJob($job, true, GearmanJobInterface::PRIORITY_LOW);
// Access the job handle string
$jobStatus->getJobHandle();
// Access the Gearman client returnCode() value
$jobStatus->getReturnCode();
if ($jobStatus->success()) {
    // Gearman client returned GEARMAN_SUCCESS 
}
```