Import more HGNC xrefs

[AntonPetrov]

Need to systematically look through all unmapped HGNC xrefs and try to add as many as possible.

Examples:

• HGNC:26327 refers to NR_026905 (obsolete, not in RNAcentral) but it has been replaced by NR_138257 (in RNAcentral).

Getting started:

docker exec -it container_id bash
source rnacentral/local/virtualenvs/RNAcentral/bin/activate
cd rnacentral/rnacentral-webcode/rnacentral/
curl -OL ftp://ftp.ebi.ac.uk/pub/databases/genenames/new/json/locus_groups/non-coding_RNA.json
python manage.py map_hgnc -i non-coding_RNA.json -t