Add CktObj, CktObjContainer, and tests
API change: use containters in Cell
Add PinContainer
Cell.cells -> owner
Cell.instances -> Owner DP
Cell.prims -> Owner DP
Cell.nets -> Owner DP
Cell.ports -> Owner DP
Instance.pins -> Owner DP
Minor tidying up
Changed intance.cell{name} to instance.ref{name}
Changed cellname to optional. Read only one library