initialize StackedConsumer

def initialize(self, num_of_paths=None, grid=None, seed=None):
        """initialize StackedConsumer"""
        super(StackedConsumer, self).initialize(grid, num_of_paths, seed)
        for c in self.consumers:
            c.initialize(grid, num_of_paths, seed)
        self.state = [c.state for c in self.consumers]