bug 89: update BoundaryDeformablePeriodic for the center of the boundary being at 0
bug 89: update BoundaryDeformablePeriodic for the center of the boundary being at 0

ajschult/etomica,ajschult/etomica,etomica/etomica,etomica/etomica,ajschult/etomica,etomica/etomica