enabled placement of actors inside hollow surface regions
prevent parent/child regions from being neighbors if one of them is a
surface pointed in the opposite direction
added check on child region that is an inner surface to ensure that
its parent is an outer surface that covers it fully
improved membrane transitions to allow transition through cases when
region on other side of membrane was not a neighbor of the starting
region. Only works if region on other side of membrane is a neighbor of
the membrane region (i.e., not in nested grandparent cases)
wrote code to potentially allow a 3D surface region that is a 3D shape
to have a 3D surface child. This is not enabled due to issues with
requiring transitions between regions that are not neighbors.