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
Added info to changelog about new form type
updated ignore files added idea files to ignore list
Merge branch 'sonata-master'