Move variants to GRCh38

[susannasiebert]

• Decide on a stop date for adding GRCh37
• Allow only addition/editing for GRCh38 coordinates
• Make CIViCbot revisions to move existing coordinates to GRCh38
• Make change so that users can manually enter the ClinGen allele registry ID and not provide coordinates. Fetch GRCh38 coordinates automatically. We will need to determine a logic for identifying the representative transcript.

Other things to decide:

• Do we want to save GRCh37 coordinates alongside GRCh38?

[susannasiebert]

See original issue here: griffithlab/civic-server#429

[kkrysiak]

Updated gnomAD only supports 38. MANE transcripts and enhancements of myvariant.info are the same.