FeatureCollection integration with Dask Dataframes

[alxmrs]

I wrote this a while ago and thought I would share it in case there is capacity to add it to EE’s Python team roadmap.

Design doc: https://docs.google.com/document/d/1Ltl6XrZ_uGD2J7OW1roUsxhpFxx5QvNeInjuONIkmL8/edit

I think Xee is a good home for this, though another package (say, dask-ee) would be good, too.