[FEATURE] Allow RESTful module to support \EntityStructureWrapper types in the buildResourceMetadataItem function.

[m4olivei]

Resolves #919.

I'm wondering if this needs to be careful about calling $this->getSubProperty()? For me it works b/c the field types that end up using this are always defined with a sub_property, eg.

$public_fields['show'] = array(
  'property' => 'field_tv_shows',
  'sub_property' => 'show',
  'resource' => array(
    'name' => 'shows',
    'majorVersion' => '1',
    'minorVersion' => '0',
  ),
);

[m4olivei]

In addition to the failing tests, I just noticed it fails with my setup as well. I believe it stems from the fact that EntityDrupalWrapper extends EntityStructureWrapper, so the if statement is catching too much.