Variant-spark

- Hail init fix

- 201, 208 Implements p-value calculation from python
- 193 Make the covariate calculation part of RF
- 200 Migrate to Spark 3.1

- 205 Add split variable count to hail output
- 131 Update Hail 0.2 support

- 131 Add support for Hail 0.2 (currently supported version is 0.2.16)
- 137 GRCh38 reference genome with Hail based Variant Spark
- 132 Migrate to spark 2.4.4
- 139 Handling of missing genotype calls

Beta release