Allow to read input from JSON

[robertodr]

We can now read input from a QCSchema-compliant JSON file:

{
    "molecule": {
        "geometry": [
            4.01376695e+00, -4.20940270e-01,  4.13283000e-03,
            2.37659705e+00, -2.06988695e+00, -7.11878700e-02,
            3.23930049e+00,  2.02346393e+00,  3.39489300e-02,
            6.09063455e+00, -5.93154800e-01,  5.36379900e-02,
            1.40721479e+00,  2.12118734e+00, -1.08338000e-02,
            -4.04214497e+00,  3.45322880e-01, -3.30928800e-02,
            -2.55773675e+00,  2.13450991e+00, -1.37099600e-02,
            -3.05560778e+00, -2.01961834e+00,  6.48213900e-02,
            -6.12485749e+00,  3.30420500e-01, -1.20082650e-01,
            -1.22314224e+00, -1.95250094e+00,  1.40055160e-01
        ],
        "symbols": ["C", "O", "O", "H", "H", "C", "O", "O", "H", "H"],
        "molecular_charge": 0,
        "molecular_multiplicity": 1,
        "atomic_numbers": [6, 8, 8, 1, 1, 6, 8, 8, 1, 1]
    },
    "model": {
        "method": "B3LYP",
        "basis": "6-31G(d)"
    },
    "keywords": {
        "bond_index": null,
        "s6": 0.0,
        "rs6": 0.0,
        "s8": 0.0,
        "a1": 0.0,
        "a2": 0.0,
        "damp": "zero",
        "threebody": false,
        "intermolecular": false,
        "pairwise": false,
        "verbose": 1
    }
}

Note that all quantities in JSON are always in atomic units.

[ringholm]

I approve but I was not requested for review :)