Support exploded genotype structs in utility functions

[Hoeze]

It would be cool if all methods working for ArrayType(StructType([calls_schema])) genotypes could work for explode(genotypes) alias StructType([calls_schema]) as well.

Example:

• genotype_states( <ArrayType(StructType([calls_schema]))> ) works
• genotype_states( <(StructType([calls_schema])> ) does not

Of course, this only applies to methods that work on each sample separately.

[henrydavidge]

Thanks, this is a great suggestion!