Add GEnergies container class.

The GEnergies container class holds objects of type GEnergy.
Use GEnergies container instead of GEnergy vector.
Add FITS file I/O support for GEnergies class.

Added the methods load(), save(), read() and write() to enable saving and loading of energies into a FITS file.
Add load constructor to GEnergies class.

The load constructor creates an instance of the GEnergies class by loading the energy information from a FITS file.
Use GEnergies class to load and attribute energy values.