Adds python interface for Kmeans and Vector3Stats

[WagnerMarcos]

🎉 New feature

Goes on top of #220

Related to #101 #210

Summary

Adds Python interface for two math classes: Kmeans and Vector3Stats. For each class a python test has been created.

Related issues and notes

Kmeans

• For the bool Cluster(int _k, std::vector<Vector3d> &_centroids, std::vector<unsigned int> &_labels) method, that takes two output arguments, a struct was created to handle this return, as we haven't been able to handle output values using references in the arguments.
• It is possible to use python lists to handle the observations.

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• Updated documentation (as needed)
• Updated migration guide (as needed)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge

[codecov]

Codecov Report

Merging #232 (c793d31) into ign-math6 (4ac81c0) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           ign-math6     #232   +/-   ##
==========================================
  Coverage      99.22%   99.22%           
==========================================
  Files             66       66           
  Lines           6162     6162           
==========================================
  Hits            6114     6114           
  Misses            48       48           

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[francocipollone]

It goes on top of PR #220

[francocipollone]

LGTM