TrackMate_: fix median filtering

The median filter was 1) not called when asked 2) not doing any
filtering. This is fixed now.
Signed-off-by: Jean-Yves Tinevez <jeanyves.tinevez@gmail.com>
TrackMate_: v2.0.3

Signed-off-by: Jean-Yves Tinevez <jeanyves.tinevez@gmail.com>