Added Network.calculateGroundStateEnergies() method.
Added Network.calculateGroundStateEnergies() method.

This method encapsulates the creation of an array of ground-state energies
for each configuration on the potential energy surface. This code is called
in a few different places, so it's better to have a method for it so that
changes made in one place are immediately propagated to others.

faribas/RMG-Py,nyee/RMG-Py,pierrelb/RMG-Py,enochd/RMG-Py,nyee/RMG-Py,chatelak/RMG-Py,comocheng/RMG-Py,enochd/RMG-Py,KEHANG/RMG-Py,faribas/RMG-Py,KEHANG/RMG-Py,nickvandewiele/RMG-Py,nickvandewiele/RMG-Py,chatelak/RMG-Py,pierrelb/RMG-Py,comocheng/RMG-Py