Apply the fraction filter to families only

[rbdavid]

Once merged, PR #151 implements the fraction filter. If set, this filter is applied to all sequences input to the workflow, not just those PFAM/InterPro family/clan IDs input via the Families path (branch B) or "Protein Family Addition Options". The latter is the intended usage.

• Develop the EFI::Import::Filter::Fraction module to check the "source" sequence metadata/attribute for "FAMILY" (or equivalent), loop over each unique family/clan ID, and apply the fraction filter on that subset of sequences.