Use SnpEff for annotations

[jsture]

We should switch to using the SnpEff applet in the UKB for annotating SNPs now that VEP is gone from the pipeline.

• Use export_vcf on the final mt after dropping all sample info.
• Write a script to run launch and run SnpEff on this VCF
• Post-process the output VCF to create .annotations file and .setlist