Make basis set optional in WavefunctionProperties

[awvwgk]

Currently, the basis must be populated when creating WavefunctionProperties, however the deeply nested data format can be hard to produce and also redundant when large numbers of calculations are run.

Is there a way to make this optional or would it be preferable to just store the returned matrices (core hamiltonian, occupation numbers, orbital energies, orbital coefficients and density matrix in extras instead)?