Add SiteFeaturizer and PairFeaturizer to featurizer module

[kaueltzen]

• create a SiteFeaturizer class that describes single site w. LOBSTER output

  • LOBSTER charges
  • sitewise BWDF
  • coordination environment info obtained from LobsterEnv as ce, csm
  • statistical ICOHP features of its bonds (min, max, mean, std..)
  • make optional to also featurize COHPCAR (b/ab percentages, ..)

• create a PairFeaturizer class that describes single interaction w. LOBSTER output

  • compute stats from the two SiteFeaturizer outputs, e.g. LOBSTER charge differences
  • also include outputs fr. SiteFeaturizers directly -> need to think about site ordering!
  • ICOHP of bond
  • make optional to also featurize COHP of bond