Add new cluster based estimator

[glpuga]

Proposed changes

Addresses #172 #258

This refactors the estimators.hpp file into separate files for common algorithms and independent mixins, and add a new estimator mixin based on clusterization.

Add new cluster based estimator.

• Splits the space in a grid and determines the accumulated weight in each cell.
• Starting from the weight peaks, it groups cells into clusters of ever decreasing weight. It creates as many clusters as needed to cover all the particle occupied space.
• Estimates mean and covariance for each.
• Returns the mean and covariance of the cluster with the highest cumulative weight.

Type of change

• [ ] 🐛 Bugfix (change which fixes an issue)
• [x] 🚀 Feature (change which adds functionality)
• [ ] 📚 Documentation (change which fixes or extends documentation)

💥 Breaking change! Explain why a non-backwards compatible change is necessary or remove this line entirely if not applicable.

Checklist

Put an x in the boxes that apply. This is simply a reminder of what we will require before merging your code.

• [x] Lint and unit tests (if any) pass locally with my changes
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] I have added necessary documentation (if appropriate)
• [x] All commits have been signed for DCO

Additional comments

Anything worth mentioning to the reviewers.

[glpuga]

@nahueespinosa PTAL to see if this is closer to what you have in mind.

[hidmic]

@glpuga can we resurrect this and merge?