Link Translatable to Translation via annotation

Usage:
Add annotation to translatable class
```php
/**
 * @ORM\Entity
 * @TranslateReference(translationClass="YourBundle\Path\To\SomeTranslation");
 */
class Some {
    use ORMBehaviors\Translatable\Translatable;
```

And to translation class
```php
/**
 * @ORM\Entity
 * @TranslateReference(translatableClass="YourBundle\Path\To\Some");
 */
class SomeTranslation {
    use ORMBehaviors\Translatable\Translation;
```

+ more flexibility in naming