Underlying handling of VCF files

[mccalluc]

I added https://raw.githubusercontent.com/igvteam/igv/master/test/data/vcf/SRP32_v4.sorted.0.vcf to the CSV. In the network log I see these requests:

GET https://raw.githubusercontent.com/igvteam/igv/master/test/data/vcf/SRP32_v4.sorted.0.vcf.idx
OPTIONS https://raw.githubusercontent.com/igvteam/igv/master/test/data/vcf/SRP32_v4.sorted.0.vcf

• If this type matters, we somehow need to ensure that the .idx is in place.
• and maybe look into the IGV code to see why it needs OPTIONS.