minor: remove unneeded uses of AddIdent.ref

ToDatomicCast can take care of this already
redesign: new traits for Tx Data identity

KeywordIdentified for AddIdent and Attribute: these are entities that are identified by keywords (although they have a :db/id as well as a :db/ident)
TempIdentified for AddFact and AddEntity: these are tx data that use possibly temporary ids
FinalIdentified for RetractFact and RetractEntity: these are tx data that use definitely final ids

this commit discover the bug reported in Issue #43