Feature 238 load_cvs()

[TheSlimvReal]

Targets issue #238.

Loading a CSV works. The CSV is always distributed along the 0 axis because only this way the file can be read in parallel.
It currently does not work with types other than float32 because of the use of balance_() and issue #329.

Question is, should the saving also be implemented or is this another issue?

[codecov-io]

Codecov Report

Merging #330 into master will increase coverage by <.01%.
The diff coverage is 96.15%.

@@            Coverage Diff             @@
##           master     #330      +/-   ##
==========================================
+ Coverage   97.06%   97.06%   +<.01%     
==========================================
  Files          53       53              
  Lines        9265     9417     +152     
==========================================
+ Hits         8993     9141     +148     
- Misses        272      276       +4

Impacted Files	Coverage Δ
heat/core/tests/test_io.py	93% <100%> (+1.2%)	⬆️
heat/core/io.py	90.25% <94.59%> (+2.82%)	⬆️
heat/core/dndarray.py	95.56% <0%> (+0.19%)	⬆️
heat/core/communication.py	93.96% <0%> (+0.31%)	⬆️

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[Markus-Goetz]

Minor issues, potentially something to discuss