Add xrefs and subsets of uniprot reference proteomes to ncbitaxon build

[cmungall]

Uniprot has ~18k reference proteomes

https://www.uniprot.org/proteomes/

these have their own UP IDs. We should add mappings to these. Note the mappings are not equivalent, the UP ID represents the proteome, but should still be 1:1.

We can also make a subset for this and have its own purl

There is also a subset used by QfO http://www.ebi.ac.uk/reference_proteomes/ we could mark these with a subset