Add QChem interface

[pbowling]

Add QChem interface (to use CDFT) from JCP B paper.

WIP: Implementation to be migrated and checked for compatibility with the latest version.

[garantes]

Hi!

This is a nice add. Note that pDynamo internal QC module can do cDFT, see for example: examples/pSimulation/ChargeRestraintEnergies.py ; And there is a pDynamo interface to PySCF, which is another QC code that can do cDFT.