Adding a resource form type

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Fixed tickets | -
| License       | MIT
| Doc PR        | No yet

I already submit a PR like that but it was a little bit different. I use resource bundle for custom development and I create this form all the time, it is really annoying! If you are agree with this I can update the Sylius's form in a other PR.
IMO good enough would be:
```php
$resolver->setDefaults(array(
    'data_class'        => $this->dataClass,
    'validation_groups' => $this->validationGroups,
));
```
Cause anyway you have validation done on resolver (if not we should add it).