Retrain BioMegatron using MedMentions with the new NodeNorm

[gaurav]

The new NodeNorm provides better information on identifiers in MedMentions, so retraining BioMegatron with these new identifiers and Biolink types might help BioMegatron make better type determinations.

[gaurav]

Chris suggested to me today that distinguishing between genes and proteins might be confusing for BioMegatron, since they are often used in similar contexts. At some point, we should try training BioMegatron without distinguishing between genes and proteins and see if that improves its accuracy (assuming it's needed after training it on the new NodeNorm).