Refactors segmentation to add analysis provider support

[mehak-sachdeva]

• [x] All declared geometries are geometry(Geometry, 4326) for general geoms, or geometry(Point, 4326)
• [x] Existing functions in crankshaft python library called from the extension are kept at least from version N to version N+1 (to avoid breakage during upgrades).
• [x] Docs for public-facing functions are written
• [x] New functions follow the naming conventions: CDB_NameOfFunction. Where internal functions begin with an underscore
• ~[ ] Analysis Documentation written (aka learn) template~ --> May do separately
• [x] If function is in Python, code conforms to PEP8 Style Guide

@stuartlynn, @andy-esch
Refactored the segmentation function to have data provider framework. Tested with a basic dataset and the model works fine. Testing it with more complex datasets and updating the test_segmentation.py subsequently.

[mehak-sachdeva]

@andy-esch : Tried mitigating the tests but it is still failing with a 'fetch' AttributeError. Could you please look into it to see what is going on and how best to proceed? Thank you! @stuartlynn : for visibility

[stuartlynn]

@andy-esch If it's easy to do we should change the name of this analysis to Random Forest Regressor as I think it more accurately describes the analysis that's being run here.

[andy-esch]

We can create some new functions that alias the originals pretty easily:

CREATE OR REPLACE FUNCTION CDB_RandomForestRegressor(...) RETURNS ... AS $$
BEGIN
RETURNS QUERY SELECT * FROM CDB_CreateAndPredictSegment(...);
END;
$$ LANGUAGE plpgsql;