[FIX] owkmeans: fix initialization choice

[markotoplak]

Issue

Initialization (random or k-means++) was wrongly passed from widget to the library.

Includes

• Code changes
• Tests
• Documentation

[lanzagar]

Nice catch. While you are fixing this, could you improve this one step further and remove the constants in the middle of the code?
I think something like changing INIT_METHODS to a dict or tuple of tuples with both our strings and scikit parameters would be much clearer and more future-proof.

[codecov-io]

Codecov Report

Merging #3090 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #3090      +/-   ##
==========================================
+ Coverage   82.42%   82.43%   +<.01%     
==========================================
  Files         335      335              
  Lines       58037    58048      +11     
==========================================
+ Hits        47838    47849      +11     
  Misses      10199    10199

[markotoplak]

@lanzagar, thank you, I did as you suggested.