Added GearmanOutputAwareInterface for worker output

This interface will be checked for when executing workers.
If the worker object implements this interface, then the output of the GearmanExecute is passed
to the worker.

Changes:

* Added the interface Mmoreram\GearmanBundle\Command\Util\GearmanOutputAwareInterface.
* Added GearmanExecute::setOutput().
* Updated GearmanWorkerExecuteCommand to add the output to GearmanExecute.
* Updated GearmanJobExecuteCommand to add the output to GearmanExecute.
* Updated documentation with example worker implementing the interface.
Fixed docs to use Driver\Gearman for annotations
escaped backslashes
escaped backslashes
Merge pull request #119 from orolin/worker_output

Added GearmanOutputAwareInterface for worker output
PHPCS fix
Applied php-formatter to all package

* Sorted all Use Statements alphabetically desc
Added php-formatter as dependency

* Also added .formatter.yml file
Changed branch-alias of dev-master to 3.0-dev
Updated composer.json to use symfony/symfony-framework >=2.4

Prior to dependency change projects using symfony 2.2 - 2.3 can use the package.
However commands will break due to commands as services being introduced in 2.4

Although this creates a BC break for composer updates, projects using this and symfony <2.4
would not have functioned properly regardless.