Implement batch calculations for ASE calculators

[TobiasDijkhuis]

Using this change, it would be possible to calculate the forces of both dimer structures, or all NEB images at the same time using an NEB calculator, by putting another function in the same file as ase_calc and _calculate.

def batch_calculate(Rs, atomicNrs, boxs, calc):
    # --- customize this section ---
    return energies, forces

I would also like the option to somehow do this using pyeonclient's potential_from_calc, but this will do for now 😄

I am not the most experienced in C++, so please let me know if I need to change anything.

[TobiasDijkhuis]

Closing in favor of #409