support for OpenTargets #16
Description
OpenTargets is an EBI project which we would like to link out to. I just added the BridgeDb record for it: bridgedb/datasources@d1311c5
They use Ensembl identifiers internally, and I like to request to add Ensembl<>OpenTargets mapping, basically both with the same ID, but with different Datasource (system code: Opt; there is no identifiers.org record, as far as I can see).