Fix MultiArray and DoubleGrid data set to use row major storage as documented

[wirew0rm]

The MultiArray container was documented to use row-major storage to be compatible with c++ and other existing code, but implemented as column major.

This PR fixes this discrepancy by using row-major.

Also DoubleGridData set had to be adapted, because the expectation here that colums correspond to the x-axis and rows to the y-axis, so the data has to be transposed here.

If they do not use the internal MultiArray type, nothing should change for end users, there are not modifications to the samples.

[codecov]

Codecov Report

Merging #329 (b088c48) into master (c0ea477) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master     #329      +/-   ##
============================================
+ Coverage     51.84%   51.85%   +0.01%     
- Complexity     7315     7318       +3     
============================================
  Files           394      394              
  Lines         41189    41197       +8     
  Branches       6627     6627              
============================================
+ Hits          21353    21364      +11     
+ Misses        18333    18332       -1     
+ Partials       1503     1501       -2     

Impacted Files	Coverage Δ	Complexity Δ
...ain/java/de/gsi/dataset/spi/DoubleGridDataSet.java	97.41% <100.00%> (+0.19%)	50.00 <8.00> (+2.00)
...main/java/de/gsi/dataset/spi/utils/MultiArray.java	74.66% <100.00%> (+2.66%)	27.00 <0.00> (ø)
...art/renderer/datareduction/DefaultDataReducer.java	63.60% <0.00%> (+0.35%)	23.00% <0.00%> (+1.00%)

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