Add missing groundings from Gilda

For downstream use of these models, having identifiers associated with each entity is important but several species are missing these identifier annotations. I wrote a script to process all the _stable.xml files in this repo and find species that are missing identifiers. I used Gilda (https://github.com/indralab/gilda) to find an appropriate grounding for these species based on their string name, and if found, add this automatically to the xml, and then re-serialize it to be able to PR the changes. In total, 423 groundings are added.