CA chart, highlight nearest points of a point

BP: aider à voir les plus proches voisins (la projection AFC étant déformante) (on aurait l'info en calculant la distance dans l'espace complet)

from txm-info : be able to define a color for points linked to other points (TBD: neighbors, correlation ?), or to draw segments linking a selected point to its nearest neighbors in the complete space (the N-dimension space vs the vizualized 2D space)