Multi-species annotation for complexes/groups #91

Based on the multispecies model for plant we're working on (@elenadelpup), we noticed the following: As the GPML2021 schema does not permit species annotations on elements, these taxa cannot be represented as DataNode annotations and are therefore absent from the species-level RDF output.

Sanity check, when using the Annotation Types, make sure that "Taxonomy" can be used on groups/complexes as well. @mkutmon