Gaussian basis set handling is distributed (and re-implemented) across 3 different spots

[blokhin]

We have a major design issue here, the three different code parts deal with more or less the same:

• pycrystal.CRYSTOUT.parse_bs_input - cumbersome code of mine, but deals with GHOST, d12 / out format
• pycrystal.parse_bs - old legacy code by @mlosev, but useful for dealing with GAUSSIAN / EMSL format
• aiida_crystal_dft.io.parsers.gto_basis_parser - concise code by @ansobolev, but too general