Partially? close #27

Hello,

I hope you are going well.

This PR proposes to update :

• The distance matrix label plot to make it more self-explanatory
• The compute_true_positives
  • change cle.maximum_y_projection to cle.sum_y_projection to correctly count ambiguous_matches
  • update to the way false positives are detected to match the new distance_matrix shape
  • Following https://arxiv.org/pdf/2206.01653.pdf recommandation (Fig 14), add ambiguous match to false positive in the F1 score
• Update the discussion about how to choose the threshold and its figure.
  
  --> I think the previous graph (in red) had errors as there are 15 annotated cells, and all detected center point should be ambiguous with a big enough threshold?

Thank you,

Clément