IGBF-1380 Support VCF4.2

Improve readability by removing commented code, and splitting long lines of arguments

Allow IGB to read VCF v4.2 and v4.3

• This does not take advantage of any added features from these versions.

Remove unused code that throws errors

Remove inaccurate file format check

• Code intent was that the first field must be 'GT', otherwise throw an error.

• This is actually not a rule. The specification (v4.1) reads: "The first sub-field must always be the genotype (GT) if it is present. There are no required sub-fields."; GT may not be present