Split megafile into fingerprinting namespace + minor refactoring

src/metabase/api/fingerprint.clj

src/metabase/fingerprinting/comparison.clj

src/metabase/fingerprinting/core.clj

src/metabase/fingerprinting/costs.clj

src/metabase/fingerprinting/fingerprinters.clj

src/metabase/fingerprinting/histogram.clj