Automunge

- remade function assemblepostprocess_assigninfill
- which serves purposes of converting user passed entries from assigninfill to final assignments to apply infill
- (conversion required because user has option to pass both source column headers and derived column headers, plus any updates based on MLinfill parameter)
- resulting function is much cleaner than prior, 100 fewer lines of code, and I think much more transparent of what is being accomplished

- moved infill application into a support function for improved modularization / generality
- found an errant data structure relic convention in postmunge(.) that was no longer needed
- so removed all instances of preFSpostprocess_dict and replaced with postprocess_dict
- (the original inclusion was kind of a hack for edge case bug that is now resolved in much much cleaner fashion)
- performed an audit of shuffle applications
- found an inconsistency between automunge(.) and postmunge(.) that was impacting validation checks
- (automunge was shuffling prior to validation split and then again after levelizer, while postmunge was only shuffling after levelizer)
- so revised automunge(.) validation split to perform any random seeding as part of scikit train_test_split instead of with seperate shuffle operation
- so now automunge(.) application of shuffletrain parameter is fully consistent with postmunge(.)
- which makes validation a little easier since now have consistent order of rows between automunge and postmunge returned sets when shuffletrain applied in conjunction with levelizer
- also removed a redundant shuffle operation for test data in automunge(.) at levelizer application
- implemented new expanded set of parameter validations for each update rollout going forward

- a tweak to convention for user specified infill with respect to interplay between MLinfill parameter and specified columns in assigninfill['stdrdinfill']
- now when MLinfill passed as True, user can designate distinct source columns or derived columns to default infills by passing to 'stdrdinfill'
- (comparable functionality was available previously by making use of assigninfill['MLinfill'], this way seemed a little more intuitive and inline with the other infill types)
- a small cleanup in imports

- performed a walkthough of the various methods based on inspection of MLinfilltype
- found a redundant inspection of MLinfilltype exterior and interior to the levelizer function calls
- consolidated to only inspect internal to function for clarity
- also cleaned up a few code comment relics in the levelizer function

- A few small revisions to feature importance evaluations in automunge(.) and postmunge(.)
- To allow continuation of processing even when feature importance halted due to edge cases (like empty label sets)

- Found a small piece that I had missed in the 3.71 scrubbing to generalize NArw, resolved