Raise error if KineticsDepository entry deals with neither reactants nor groups.
Raise error if KineticsDepository entry deals with neither reactants nor groups.

Also made it return the entry as well as save it.
chatelak/RMG-Py,faribas/RMG-Py,chatelak/RMG-Py,pierrelb/RMG-Py,nyee/RMG-Py,nickvandewiele/RMG-Py,enochd/RMG-Py,enochd/RMG-Py,KEHANG/RMG-Py,comocheng/RMG-Py,KEHANG/RMG-Py,comocheng/RMG-Py,faribas/RMG-Py,pierrelb/RMG-Py,nickvandewiele/RMG-Py,nyee/RMG-Py