Added utility function: determineBlockShape()
Refactored OpTrainRandomForestBlocked into multiple operators:
- OpFeatureMatrixCache: Extracts label points and features into a feature matrix, and CACHES them blockwise.
- OpConcatenateFeatureMatrices: Concatenate the output of OpFeatureMatrixCache for multiple images
- OpTrainFromFeatures: Simply train the RF using the feature matrix (and max label)
These changes were originally proposed in ilastik/ilastik#768.
TODO: Provide progress notifications.
OpTrainRandomForestBlocked, OpFeatureMatrixCache: Progress reporting.
Added code cleanup to-dos.
Merge branch 'feature-matrix-cache'