TrackMate_: properly de-register TrackScheme on window closing

Signed-off-by: Jean-Yves Tinevez <jean-yves.tinevez@pasteur.fr>
TrackMate_: add a SpotCollection.search(int ID) method

Signed-off-by: Jean-Yves Tinevez <jean-yves.tinevez@pasteur.fr>
TrackMate_: fix a severe bug in the model when removing/adding internal edges

Internal edges are edges that connect two spots that are connected via
another path as well, as it may happens when dealing with both splitting
and merging.
Noticed by Jan Brocher
Signed-off-by: Jean-Yves Tinevez <jean-yves.tinevez@pasteur.fr>