Add population_genotype data to variation endpoint

This adds the population genotype frequencies and counts for variation. I've removed the duplicate lines from t/test-genome-DBs/homo_sapiens/variation/genotype_code.txt too.

How's that?

On 31/10/2014 15:34, Kieron Taylor wrote:
>
> In lib/EnsEMBL/REST/Model/Variation.pm:
>
> > @@ -180,6 +181,32 @@ sub pops_as_hash {
> >    return $population;
> >  }
> >
> > +## Genotype frequencies in available populations
> > +sub PopulationGenotypes {
>
> These things have a nasty habit of propagating. It's best if you nip 
> it in the bud before someone else copies it again. Sadly I can't find 
> the coding style guide any more, so you'll just have to take my word 
> for it.
>
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> <https://github.com/Ensembl/ensembl-rest/pull/28/files#r19673443>.
>