added new method to retrieve the AlleleFeature associated with the VariationFeature in the StrainSlice object, mainly for use in web
added new method to retrieve the AlleleFeature associated with the VariationFeature in the StrainSlice object, mainly for use in web

mjg17/ensembl,Ensembl/ensembl,mjg17/ensembl,james-monkeyshines/ensembl,muffato/ensembl,at7/ensembl,mjg17/ensembl,james-monkeyshines/ensembl,muffato/ensembl,willmclaren/ensembl,at7/ensembl,at7/ensembl,willmclaren/ensembl,danstaines/ensembl,mjg17/ensembl,at7/ensembl,james-monkeyshines/ensembl,muffato/ensembl,muffato/ensembl,Ensembl/ensembl,danstaines/ensembl,Ensembl/ensembl,Ensembl/ensembl,danstaines/ensembl,james-monkeyshines/ensembl