refactor Genome::File::{Vcf,Vep} to share common code

through a new base class Genome::File::TypedStream. future formats
(e.g., BedPe) can use this as well.
Added --vcf-sample-name option to gmt varscan consensus
Added to gmt varscan consensus tests
Added Model/TestHelpers.pm to assist with testing
Make Model-build_requested.t use Model/TestHelpers
Make Model/Pair.t use Model/TestHelpers instead of live database entries

It is wrong to use database entries in our tests.
Updated class browser cache.
Updated `genome` tab completion.
Updated `gmt` tab completion.
'use base' instead of @ISA in GF:Vep:Reader
Add test for 'peek' method in vcf reader.

Sometimes, you just want to have a look at the next entry without
taking it.