Initial commit of expander code.

This code is adapted from https://github.com/googlegenomics/bigquery-examples/tree/master/pgp/provenance#gvcf_variants_expanded-table with field names updated to match the v1beta2 BigQuery schema for variants.
Updates per usage of BigQuery connector with Hadoop Streaming.
Bug fix for a ref-block and variant at the same position.

Also trimmed some unnecessary data from the unit tests.
Bug fix for private variants query.

It was not handling 1/2 genotypes correctly - neglected to merge with single alternate record.

Also added more fields to the ORDER BY clause for a few queries to keep the result sort stable across runs.