Don't put AND before conditions anymore
Remove commas from generated SQL, make anything larger than first group NULL
group_cols should be required in params, filter_cols are optional
If git is about, use it to generate a pretty diff
Deletes should take into account case_study_id and data_source
Not populating sample's case_study_id
C+P ages error, move generator to end for easier comparisons
Adapt mfdb_meanlength & mfdb_meanlength_stddev to work with new grouping function