Vibrational frequency request/response scaffolding

[tommyh-ECL]

Need to define request (e.g. VibrationalEnergyRequest) and response (e.g. VibrationalEnergyResponse) structures that allow users to calculate vibrational frequencies and eigenvectors/modes. Request packet needs to contain enough information to run a vibrational calculation for a given molecule. The response packet needs to contain, at minimum, the vibrational energies and mode vectors.