[RFC] Removed constants added BootstrapHelper

This is a first PR into making the testing component more flexible.

- Removed the `.php` dist files

I propose we do the following instead:

````php
<?php

use Symfony\Cmf\Component\Testing\HttpKernel\TestKernel;
use Symfony\Component\Config\Loader\LoaderInterface;

class AppKernel extends TestKernel
{
    public function configure()
    {
        $this->requireBundleSets(array(
            'default',
        ));

        $this->addBundles(array(
            new Symfony\Cmf\Testing\TestBundle\TestBundle(),
        ));
    }

    public function registerContainerConfiguration(LoaderInterface $loader)
    {
        $loader->load(BootstrapHelper::getDistFile('framework.yml'));
        $loader->load(BootstrapHelper::getDistFile('doctrine_phpcr_odm.yml'));
        $loader->load(BootstrapHelper::getDistFile('sonata_admin_full_stack.yml'));
        $loader->load(__DIR__ '/config/mybundle.yml');
    }
}
````
I think we should make this instead into a YAML file and document how to add the few lines of code to add extra mappings to the users own configuration file.