Integration of pyFlowSOM with current ark codebase

[ngreenwald]

Is your feature request related to a problem? Please describe.
Zak is almost done updating pyFlowSOM to be fully native in python. Once he does, it will be up to us to integrate it with the existing Pixie codebase.

Describe the solution you'd like
We'll need to decide the format of the new python-only functions which call map_data_to_codes for both the pixel and cell notebooks, what the tests will look like, and which code (including much of the mocking for R) can be deleted. You should talk with @cliu72 to make a plan so that we're ready to go once Zak is done.