Addition of the function cleaning_cluster_population

[ChiaraLionello]

I have created the function the works for 2D and 3D labels' arrays. It cleans the clusters with low population.
Solved #136

[matteobecchi]

These are the labels, not the data... aren't they always a 2D array? Each atom at each frame has one integer label, even if the data were multivariate.

[matteobecchi]

For the same reason, I think all the logic in the function for the 3D case is never necessary.

[ChiaraLionello]

I think it depends how we do want to use this function. I've thought different applications:

• 2D labels: cleaning the labels to color the trajectory
• 2D labels: can come also from other clustering methods, not necessarily from onion, and can be used as above
• 3D labels: come from get_onion_analysis and can be use to redo the plot with the number of clusters and the unclassified fraction cleaned. By keeping this function out from get_onion_analysis you are free to change the threshold how many times you want without running the Onion calculation multiple times. In this case, I should also think a way to do that plot again. On the other hand, it's true that's enough to keep only the 2D option and then run it in a for cicle when we need it.

There's no problem for me to delete it in case; since it wasn't difficult to do I've added both the options.

[matteobecchi]

Same as before, labels are always 2D.

[SimoneMartino98]

Just two easy comments. I’ll leave the discussion on the label dimensions to @matteobecchi.

Anyway, nice work!

[ChiaraLionello]

I've done everything that Simone asked.
I've talked with Matteo, and the 3D option makes sense.