Add link utility to link Symfony UX packages to existing Symfony project

[Kocal]

Q	A
Bug fix?	no
New feature?	no
Tickets	Fix #40
License	MIT

This PR add a new link utility to link Symfony UX packages to an existing Symfony project. It's literally a copy/paste from the link utility from symfony/symfony but with different directories and an explicit dependency on Symfony Filesystem component.

Demo:

[Kocal]

Looks like some of Turbo tests are not passing because of ClearMetadataCacheDoctrineCommand already defines an option em:

➜  app git:(GH-40) ✗ php public/index.php doctrine:schema:create -v
[critical] Error thrown while running command "'doctrine:schema:create' -v". Message: "An option named "em" already exists."


In InputDefinition.php line 234:
                                                        
  [Symfony\Component\Console\Exception\LogicException]  
  An option named "em" already exists.                  
                                                        

Exception trace:
  at /home/hugo/workspace-os/symfony-ux/src/Turbo/vendor/symfony/console/Input/InputDefinition.php:234
 Symfony\Component\Console\Input\InputDefinition->addOption() at /home/hugo/workspace-os/symfony-ux/src/Turbo/vendor/symfony/console/Command/Command.php:442
 Symfony\Component\Console\Command\Command->addOption() at /home/hugo/workspace-os/symfony-ux/src/Turbo/vendor/doctrine/doctrine-bundle/Command/Proxy/CreateSchemaDoctrineCommand.php:26
 Doctrine\Bundle\DoctrineBundle\Command\Proxy\CreateSchemaDoctrineCommand->configure() at /home/hugo/workspace-os/symfony-ux/src/Turbo/vendor/symfony/console/Command/Command.php:112
 Symfony\Component\Console\Command\Command->__construct() at /home/hugo/workspace-os/symfony-ux/src/Turbo/vendor/doctrine/orm/lib/Doctrine/ORM/Tools/Console/Command/AbstractEntityManagerCommand.php:18
 Doctrine\ORM\Tools\Console\Command\AbstractEntityManagerCommand->__construct() at /home/hugo/workspace-os/symfony-ux/src/Turbo/Tests/app/var/cache/dev/ContainerD6A5oeA/getDoctrine_SchemaCreateCommandService.php:26
 ContainerD6A5oeA\getDoctrine_SchemaCreateCommandService::do() at /home/hugo/workspace-os/symfony-ux/src/Turbo/Tests/app/var/cache/dev/ContainerD6A5oeA/App_KernelDevDebugContainer.php:297
 ContainerD6A5oeA\App_KernelDevDebugContainer->load() at /home/hugo/workspace-os/symfony-ux/src/Turbo/vendor/symfony/dependency-injection/Container.php:441
 Symfony\Component\DependencyInjection\Container->getService() at /home/hugo/workspace-os/symfony-ux/src/Turbo/vendor/symfony/dependency-injection/Argument/ServiceLocator.php:42
 Symfony\Component\DependencyInjection\Argument\ServiceLocator->get() at /home/hugo/workspace-os/symfony-ux/src/Turbo/vendor/symfony/console/CommandLoader/ContainerCommandLoader.php:45
 Symfony\Component\Console\CommandLoader\ContainerCommandLoader->get() at /home/hugo/workspace-os/symfony-ux/src/Turbo/vendor/symfony/console/Application.php:554
 Symfony\Component\Console\Application->has() at /home/hugo/workspace-os/symfony-ux/src/Turbo/vendor/symfony/console/Application.php:643
 Symfony\Component\Console\Application->find() at /home/hugo/workspace-os/symfony-ux/src/Turbo/vendor/symfony/framework-bundle/Console/Application.php:116
 Symfony\Bundle\FrameworkBundle\Console\Application->find() at /home/hugo/workspace-os/symfony-ux/src/Turbo/vendor/symfony/console/Application.php:255
 Symfony\Component\Console\Application->doRun() at /home/hugo/workspace-os/symfony-ux/src/Turbo/vendor/symfony/framework-bundle/Console/Application.php:82
 Symfony\Bundle\FrameworkBundle\Console\Application->doRun() at /home/hugo/workspace-os/symfony-ux/src/Turbo/vendor/symfony/console/Application.php:167
 Symfony\Component\Console\Application->run() at /home/hugo/workspace-os/symfony-ux/src/Turbo/Tests/app/public/index.php:22

This option em is now defined in Doctrine's MetadataCommand in 2.9, but is not present in 2.8.

I've forced doctrine/orm to version ~2.8.0 until doctrine-bundle is fixed (doctrine/DoctrineBundle#1327).

[weaverryan]

This is a nice idea!

[maxhelias]

It's nice to have that here too

[weaverryan]

Thanks @Kocal!