Plugin for retrieving variation data from VCFs

This plugin tells the Variation API to use VCFs
in place of or alongside the DB for fetching genotype
data. Its current use case is for the 1000 genomes
phase 3 data.

To use it, you must set up the JSON config file (see
ensembl-variation/modules/Bio/EnsEMBL/Variation/DBSQL/vcf_config.json
for an example), and set the ENABLED flag in
conf/ini-files/MULTI.ini to 1 (use both VCF and DB)
or 2 (use only VCF).