Add option to get_taxa_by_id() to get current taxon in the event of a taxonomy change

[JWCook]

This would be the case where is_active=False and current_synonymous_taxon_ids contains exactly one result. In other words, a simple 1:1 change where the requested taxon has been replaced with a different one.

In the case of a many:1 or 1:many change (or more complicated many:many revision), a warning should be logged.