Feature 464. Add Post Status support in post meta conditions

[lopandpe]

Added support for the post_status condition. This allows adding a post_status (e.g., draft, publish, etc.) to the 'where' clauses on the container.

Container::make('post_meta', 'My container')
	->where('post_type', '=', 'book')
	->where('post_status', '=', 'publish')
	->add_fields(array(

		Field::make('text', 'book_field1', __('My field only visible on published books'),
	));