Support aliases for systemCode for webservice

[ariutta]

To make the webservice easier to use, let's look into supporting aliases for systemCode for the webservice. This can be broken into two parts:

1. support conventionalName (e.g., Entrez Gene)
2. support Miriam namespace (e.g., ncbigene) and identifiers.org IRI (e.g., http://identifiers.org/ncbigene/)

The first one should be easy to set up, because it already works for all endpoints except possibly xrefsBatch. But it needs to be tested with the all variations of xrefsBatch.

The second one would be a little more involved. It would mean returning the same results for all of the following endpoints:
http://webservice.bridgedb.org/Human/xrefs/L/1234
http://webservice.bridgedb.org/Human/xrefs/Entrez%20Gene/1234
http://webservice.bridgedb.org/Human/xrefs/ncbigene/1234
http://webservice.bridgedb.org/Human/xrefs/http%3A%2F%2Fidentifiers.org%2Fncbigene%2F/1234

[egonw]

@Chris-Evelo, we earlier this week discussed support for this. I't been on the schedule for a while now.

[Chris-Evelo]

Would be really good indeed. Think the last one should also work in the "www" form