Major scrattch.taxonomy update - KL divergence

[jeremymiller]

Major update to scrattch.taxonomy with the following changes:

• Inclusion of KL divergence code and associated Core/I1/I2/I3/PoorQ QC calls
• Rerouting all links to external files back to locations in the anndata variable
• Changes to components of anndata variable to allow for above (ideally with back-compatibility)
• Minor error correction throughout
• Some minor documentation updates
• Also: Creation of a DRAFT aligned schema between AIT format and other formats (e.g., cell annotation schema, BKP, cellxgene)