[WIP - do not merge!] Move sparkdl utilities for conversion between numpy arrays and image schema to ImageSchema

[tomasatdatabricks]

[WIP] Preparation for moving stuff to Spark.

Moved utilities for image schema <=> numpy array conversion to (copy pasted from spark 2.3) Image schema code.

1. Extended ImageSchema scala code with support/information for all OpenCv modes
2. python toNDArray and toImage utilities extended to work with all supported data types.
3. [minor] sparkdl toImage function included batch size stripping - had to make a separate call for that

[codecov-io]

Codecov Report

Merging #90 into master will increase coverage by 1.43%. The diff coverage is 77.46%.

@@            Coverage Diff             @@
##           master      #90      +/-   ##
==========================================
+ Coverage   82.49%   83.92%   +1.43%     
==========================================
  Files          33       33              
  Lines        1879     1866      -13     
  Branches       35       39       +4     
==========================================
+ Hits         1550     1566      +16     
+ Misses        329      300      -29

Impacted Files	Coverage Δ
python/sparkdl/udf/keras_image_model.py	75.6% <0%> (+1.8%)	:arrow_up:
...main/scala/com/databricks/sparkdl/ImageUtils.scala	90.9% <100%> (ø)	:arrow_up:
...n/sparkdl/estimators/keras_image_file_estimator.py	74.35% <100%> (ø)	:arrow_up:
python/sparkdl/transformers/tf_image.py	94.06% <33.33%> (-0.05%)	:arrow_down:
python/sparkdl/param/image_params.py	81.81% <50%> (+6.14%)	:arrow_up:
.../scala/org/apache/spark/ml/image/ImageSchema.scala	77.94% <75%> (-1.1%)	:arrow_down:
python/sparkdl/image/imageIO.py	73.33% <81.25%> (-4.77%)	:arrow_down:
python/sparkdl/image/image.py	78.82% <82.35%> (+40.58%)	:arrow_up:

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[tomasatdatabricks]

@sueann Yes I agree, I would merge spark version first and merge this one only after spark 2.4 is released. I made the PR here mostly because that's what we need the changes for, so it can be reviewed in context, also to run tests.

I'll mark it WIP.

[sueann]

ah ok got it. thanks!