Large API refactoring: introducing spark3D 0.3

[JulienPeloton]

This PR introduces the new spark3D API.

Previously on spark3D

The previous versions (0.1, 0.2) had several limitations:

• Use (low-level) RDD API
• Many custom objects exposed
• Interface Scala/Python unsatisfactory (several JavaObjects left)

And now...

spark3D should be viewed as an extension of the Apache Spark framework, and more specifically the Spark SQL module, focusing on the manipulation of three-dimensional data sets:

• DataFrame API
• Extension of the Spark SQL module (new methods + implicits on DataFrame)
• Metadata are propagated (not just 3D coordinates).
• Seamless interface with Python

The focus is now done on repartitioning. The biggest feature as of now is the possibility to perform exact DataFrame repartitioning via df.repartitionByCol.

More to come with this PR.

[codecov-io]

Codecov Report

Merging #108 into master will decrease coverage by 9.52%. The diff coverage is 84.34%.

@@            Coverage Diff             @@
##           master     #108      +/-   ##
==========================================
- Coverage   96.37%   86.84%   -9.53%     
==========================================
  Files          32       29       -3     
  Lines        1240     1140     -100     
  Branches      218      201      -17     
==========================================
- Hits         1195      990     -205     
- Misses         45      150     +105

Flag	Coverage Δ
#python	93.63% <ø> (-0.68%)	:arrow_down:
#scala	84.07% <84.34%> (-13.18%)	:arrow_down:

Impacted Files	Coverage Δ
...ark3d/spatialPartitioning/SpatialPartitioner.scala	0% <0%> (-20%)	:arrow_down:
...m/spark3d/spatialPartitioning/KeyPartitioner.scala	100% <100%> (ø)
...park3d/spatialPartitioning/OctreePartitioner.scala	43.75% <100%> (-56.25%)	:arrow_down:
src/main/scala/com/spark3d/utils/GridType.scala	100% <100%> (ø)	:arrow_up:
...main/scala/com/spark3d/python/PythonClassTag.scala	100% <100%> (ø)	:arrow_up:
src/main/scala/com/spark3d/package.scala	100% <100%> (ø)
src/main/scala/com/spark3d/Checkers.scala	100% <100%> (ø)
src/main/scala/com/spark3d/Partitioners.scala	87.03% <73.91%> (ø)
src/main/scala/com/spark3d/Repartitioning.scala	80.43% <80.43%> (ø)
...spark3d/spatialPartitioning/OnionPartitioner.scala	48.33% <92.85%> (-42.98%)	:arrow_down:
... and 16 more

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[JulienPeloton]

Merging this first stable interface. Version number has not been bumped yet.