data_store follow-ups

[eseiler]

1: void data_store::validate()

• We need to test whether data_store is set up correctly before we start executing hierarchical binning.

2: Refactor data_store

• If config is stored in data_store, the data_store can get a constructor that initialises some members, e.g., the FPR correction, via IIILE. This would be more error proof.
• The data_store is not very intuitive (and should be restructured) because it contains members that:
  • are given externally and are always const
  • are given externally but change in recursive calls (e.g. positions)
  • are local but const
  • are local but will change in iterations of the DP (e.g. union_estimation)

Originally posted by @smehringer in #224 (comment)