Replace MyGene API with BioThings client in WF2

[kennethbruskiewicz]

Right now WF2's setup requires the MyGene client, and drawing the MyGene client from PyPI gives you a blank MyGene object which makes the code fail to import the module.

It seems like that the team deprecated MyGene Client for a more general BioThings client.
biothings/mygene.py#7

Replace the MyGene client with the BioThings client and test the outcome.

[newgene]

I tested pip install -r requirements.txt locally, it installs mygene module correctly and import mygene works fine for me as well.

The requirements.txt is from here

mygene module now depends on biothings_client, but it should be transparent. biothings_client module will be installed automatically.