'Unstash some states. This is an alias for move(), with defaults for the stashes.
:param filter_func: Unstash states that match this filter. Should be a function that takes a state and returns
True or False. (default: unstash all states)
:param from_stash:  take matching states from this stash. (default: \'stashed\')
:param to_stash:    put matching states into this stash. (default: \'active\')
:returns:            The resulting SimulationManager.
:rtype:             SimulationManager'

def unstash(self, filter_func=None, to_stash=None, from_stash=None):

    to_stash = ('active' if (to_stash is None) else to_stash)
    from_stash = ('stashed' if (from_stash is None) else from_stash)
    return self.move(from_stash, to_stash, filter_func=filter_func)
