TrackMate_: use the new imglib2 local extrema finder in LoG detector

Signed-off-by: Jean-Yves Tinevez <jean-yves.tinevez@pasteur.fr>
TrackMate_: multithreaded tests for the new LoG detector

We proved that it cannot work as it is: FFTConvolution is multithreaded
and does not let you configure the number of threads it uses.
A pull request in imglib2 has been made.
Signed-off-by: Jean-Yves Tinevez <jean-yves.tinevez@pasteur.fr>