Dev branch is now dependent on impropers/donors/acceptors/NNB/NGRP being defined in the psf.

[GregorySchwing]

Describe the bug
When adding the ability to read and write impropers/donors/acceptors/NNB/NGRP for hybrid MCMD, we have become dependent on these terms existing in the PSF. We previously didn't require their definition, so if not found the same flexibility should still exist to set them as

    0 !NIMPHI: impropers


    0 !NDON: donors


    0 !NACC: acceptors


    0 !NNB


    0 !NGRP

To Reproduce
Run ~/GOMC_Examples/NPT/water_580_00_K with development branch NPT ensemble

Expected behavior
Run even though impropers/donors/acceptors/NNB/NGRP are missing, since GOMC doesn't even support these terms in the energy calculation.

Please complete the following information:

• OS: [Ubuntu]
• Ensemble: [NPT]
• Code version [2.70 dev]