Add fixtures directory and files

Did a fresh install, and missing fixtures directory and files were missing, might be good to add them, as the exception was not obvious...

    [Symfony\Component\Debug\Exception\ContextErrorException]                                                                                                                                                 
    Notice: Undefined index: Sylius.Image.book in /home/user/project/project_master/vendor/doctrine/data-fixtures/lib/Doctrine/Common/DataFixtures/ReferenceRepository.php line 145