dpxdt revival

This creates a fresh DB every time you run `dpxdt update`. It gets populated from `schema.sql` and a SQL database dump.

Check out the new README.md for more details.
Previously it required the file to be on HDFS. Loading local VCFs was something we support pre-migration with `ALLOW_LOCAL_VCFS`. This restores that ability. It's helpful for loading a VCF file from local disk into CycleDash, e.g. the `tests/js/data/snv.vcf` file I loaded for dxpdt testing.