TrackMate_: fix inconsistency in the row headers of TrackScheme

Signed-off-by: Jean-Yves Tinevez <jean-yves.tinevez@pasteur.fr>
MaMuT_: skeleton of a flexible way to handle key bindings

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