Generalize runNEB command in QMReaction class

This was previously done, but was too general so it
was not functional later. This should now use a
`setCalculator` method which should reside in the
child classes that sets up the specific calcular
(Mopac, Gaussian) to work with the NEB class in ASE.
Setup the gaussian calculator to work with ASE

The NEB class requires a calculator to be specified for each image.
This cycles through the necessary images and sets up gaussian for
ASE.