Extension to include BridgeDB

BridgeDB provides some mappings. It's based on Identifers.org (however it uses only the primary resource and not the alternative resources).
If we included in the widget, we might generate more links.

Widget input:
taxonId (e.g. 9606) or organism name (at least initially), if it's easier
LUI (e.g. ensembl:400500)
type (Gene or Protein)

[Here](https://www.bridgedb.org/swagger/#!/Genes/get_organism_xrefs_systemCode_identifier) the endpoint to call in bridgedb
It can be called for Protein and Gene. The organism in input is the organism name (not the taxonId :()
[Here](https://www.bridgedb.org/documentation/system-codes/) all the system codes. As system code, we will only use **L** (for genes) and **S** (for proteins).

Example: curl -X GET --header 'Accept: */*' 'https://webservice.bridgedb.org/Homo%20sapiens/xrefs/L/400500'

The endpoint doesn't return the urls :( but only the identifiers.
In the bridgedb github repo, in the [datasources.xml file](https://github.com/bridgedb/BridgeDb/blob/series/2.3/org.bridgedb.bio/resources/org/bridgedb/bio/datasources.txt), we can retrieve the URL pattern.