Use multiple threads when loading existing VCF files in the genotype QC wizard

[Nicklas Nordborg]

This could save some time when running this wizard.

[Nicklas Nordborg]

In [7071]

Referenes #1470: Use multiple threads when loading existing VCF files in the genotype QC wizard

The VCF files are now parsed by separate threads. Unfortunately we don't gain that much. It seems to be because getting the reference to the actual VCF file requires additional database queries which takes about the same amount of time as the parsing. So the parsing threads will have to wait for the next file and it doesn't help if we have more than 2.

I think it should be possible to improve this if we can get some functionality into the BASE core API for loading AnyToAny links. See ​https://base.thep.lu.se/ticket/2296

[Nicklas Nordborg]

In 7073:

References #1470: Use multiple threads when loading existing VCF files in the genotype QC wizard

Changed the implementation to use the FastLinkLoader API introduced in BASE 3.19.8.