Added __mul__() method for combining KineticsData objects.
Added __mul__() method for combining KineticsData objects.

This is similar to the __add__() method of ThermoData objects, except
that we multiply rate coefficients instead of adding them.

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