Option to use energy above hull #13

Add argument in create and update which is list of energy above convex hull values.

This can be used in place of the formation energy weighting for the formation of the gDFs.

This allows people to use other methods to identify the energy above the hull, rather than it being directly implemented in RAFFLE yet.

Additionally, this means that gvector_type needs to have an element called "energy_above_hull", as well as gvector_container_type having a logical (default to false) called "weight_by_hull".