Improve GO term provenance

[AntonPetrov]

Currently Rfam families are associated with GO terms but no additional metadata is captured. It would be useful to provide the following for all GO terms:

• Qualifier (especially important if it is 'NOT’)
• Reference (e.g. PubMed ID or a GO_REF describing how the annotations were made)
• Evidence code
• Date
• Assigned by

Documentation: ftp://ftp.ebi.ac.uk/pub/databases/GO/goa/HUMAN/README

If implemented, the information can be propagated to RNAcentral.