[Form] Adding attributes to ChoiceView

Description:
Because some times is usefull to add some attributes to select's options. Exemple when using, select2, chosen, or juste by adding some prototypes.

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #5286
| License       | MIT


Example : 

```php
    $builder->add('test2', 'choice', array(
            'choices' => array(
                'male' => 'MALE',
                'female' => 'FEMALE'
            ),
            'choices_attributes' => array(
                 array('titi' => 'toto'),
                 array('foo' => 'bar')
            ),
            // OR
            'choices_attributes' => function(ChoiceListInterface $choices) {
                $att = array();
                foreach ($choices->getChoices() as $choice) {
                    $attr[] = array('foo' => 'data from another place' . $choice);
                }

                return $attr;
            },
            'choices_prototypes' => array(
               array('name' => 'toto', 'form' => new ContactType(), 'options' => array())
            )
            // OR
            'choices_prototypes' => function(ChoiceListInterface $choices) {
                $protos = array();
                foreach ($choices->getChoices() as $choice) {
                    $protos[] = array('name' => 'advanced', 'type' => new ContactType($choice));
                }

                return $protos;
            }
        ));
```