Change schema to return gateway objects
Comment out unused code in the Axiom monkey patch

* This code will probably be needed when this is implemented
  properly in Axiom core, but for now we don't need it.
Add YARD docs to Axiom::Relation::Base
Update flay and flog thresholds
Add comment to class
Kill mutation in Axiom::Adapter::Memory::Gateway#update
Kill mutation in Axiom::Adapter::Memory#gateway