support for querying HGVSc alongside ensembl transcript IDs

[FelixMoelder]

When using ProVar for querying variants we noticed that it is not support to search for variants by providing a ensembl transcript ID and a HGVSc value. Instead we are advised to provide a RefSeq ID alongside the HGVSc entry.
As VEP performs HGVSc annotation by returning a ensembl transcript ID together with the HGVSc entry it would be helpful if this combination could also be used for querying ProtVar.