TrackMate_: make the LogDetector explicitely multi-threaded

Even if in practice, we do not use its multi-threading capability. It is
not ok to let the user believe it is single threading whether in its
core it is not.
Also the code needs some more polishing.
Signed-off-by: Jean-Yves Tinevez <jean-yves.tinevez@pasteur.fr>
TrackMate_: make the CropIgView more re-usable

Signed-off-by: Jean-Yves Tinevez <jean-yves.tinevez@pasteur.fr>
TrackMate_: convenience comparator for Spot

Signed-off-by: Jean-Yves Tinevez <jean-yves.tinevez@pasteur.fr>
MaMuT_: a semi-automated tracking method

How to use:
- Manually add a spot, and adjust its radius so that it is meaningful.
- Select this spot and only this one.
- Press Shift-A.
- Benefit.
Signed-off-by: Jean-Yves Tinevez <jean-yves.tinevez@pasteur.fr>