Form type : sonata_choice_field_mask

Copied from SonataDoctrinePhpcrAdminBundle
This widget allow to hide/display other fields in a form when a value in a select widget  is selected.
sonata_type_choice_field_mask_widget : javascript change

- Hide all fields if no item is selected
- Use jQuery instead of $
Merge pull request #2410 from jerome-fix/ChoiceFieldMaskType

Form type : sonata_choice_field_mask