Convert PcaTransform to Estimator API (#1333)

* Added placeholder

* Cleaned up Infos (replaced with ColumnPairs)

* Added ColumnInfo

* Added all the Create() methods.

* Added Mapper

* Commented out the EntryPoint

* Added PcaEstimator2

* PcaWorkout test passes

* Added pigsty api

* Fixed EntryPoint

* Fixed the arguments

* Fixed tests and added pigsty test

* Deleted Wrapped PCA transform

* Float -> float

* Cleaned docstrings

* Removed some unnecessary checks

* Simplified unnecessary code

* Moved some fields to ColumnInfo for simplifications

* Simplified weight columns

* Address PR comments #1

* Addressed PR comments #2

* Moved the static test

* PR comments #3

* Moved schema related information out of ColumnInfo and into Mapper.ColumnSchemaInfo.

* PR comments

* PR comments

* Updated manifest for entrypoint PcaCalculator

* Fixed schema exceptions