Added two methods for deep copying SSSR
Added two methods for deep copying SSSR

Deep-copying occurs by creation of new submol objects
in the previously written methods convertRingToSubMolecule
and combineTwoRingsIntoSubMolecule functions.
Then it gets reconverted into lists of atoms like the original
inputs.

pierrelb/RMG-Py,pierrelb/RMG-Py