This PR was merged into the 1.2-dev branch.

Discussion
----------

Service Task support

| Q             | A
| ------------- | ---
| Branch?       | `master`
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | -
| Fixed tickets | -
| License       | BSD-2-Clause

This PR adds the Service Task support.

When a Service Task is reached in the process, the task will be allocated and started automatically, and the associated Symfony service is executed at the `started` state on the work item. And the task will be completed automatically.

Symfony services for this must implement `PHPMentors\Workflower\Workflow\Operation\OperationRunnerInterface` as the following:

```php
<?php
...
use PHPMentors\Workflower\Workflow\Operation\OperationalInterface;
use PHPMentors\Workflower\Workflow\Operation\OperationRunnerInterface;
use PHPMentors\Workflower\Workflow\Workflow;
use PHPMentors\WorkflowerBundle\Workflow\Participant\SecurityParticipant;
use PHPMentors\WorkflowerBundle\Workflow\Participant\SecurityParticipantAwareInterface;

class ...OperationRunner implements OperationRunnerInterface, SecurityParticipantAwareInterface
{
    private $securityParticipant;

    public function setSecurityParticipant(SecurityParticipant $participant)
    {
        $this->securityParticipant = $participant;
    }

    public function provideParticipant(OperationalInterface $operational, Workflow $workflow)
    {
        return $this->securityParticipant;
    }

    public function run(OperationalInterface $operational, Workflow $workflow)
    {
        ...
    }
}
```

And the Symfony service for an operation runner should be tagged as `phpmentors_workflower.operation_runner` with `phpmentors_workflower.security_participant_aware` as the following:

```yaml
    ..._operation_runner:
        ...
        tags:
            - { name: phpmentors_workflower.operation_runner }
            - { name: phpmentors_workflower.security_participant_aware }
```

Commits
-------

441f3f9 change the scope of `phpmentors_workflower.security_participant` to the container scope
31577ff add support for Service Tasks by the service tag `phpmentors_workflower.operation_runner`

…y instead of the `OperationRunnerInterface` collection #8

… the tag 'phpmentors_workflower.security_participant_aware' #8