Fix bug preventing to have V stats after two spots.

Signed-off-by: Jean-Yves Tinevez <jean-yves.tinevez@pasteur.fr>
Draw the V vs I plot.

Signed-off-by: Jean-Yves Tinevez <jean-yves.tinevez@pasteur.fr>
Don't use a PerTrackColorGenerator for the VvsI plot.

It registers as a model listener, and is a bit overkill.
Signed-off-by: Jean-Yves Tinevez <jean-yves.tinevez@pasteur.fr>
Draw the histograms for track intensity and velocity on overlay.

Signed-off-by: Jean-Yves Tinevez <jean-yves.tinevez@pasteur.fr>