Clarify that gene/transcript IDs are Ensembl IDs

[nawatts]

Genes and transcripts currently have generically named ID fields gene_id and transcript_id. ensembl_gene_id and ensembl_transcript_id fields should be added to clarify that these are Ensembl genes/transcripts.

[nawatts]

We want to be able to use the same GraphQL types for both Ensembl and RefSeq genes/transcripts.

Genes should have both ensembl_id and refseq_id fields. The generic gene_id should reflect whichever type is requested.

Transcripts can have just the generic transcript_id field, which would be either Ensembl or RefSeq based on which type was requested.