Release v2.2.0-rc4

Signed-off-by: Jean-Yves Tinevez <jeanyves.tinevez@gmail.com>
Merge branch 'master' of ssh://github.com/fiji/TrackMate
Merge branch 'master' of ssh://github.com/fiji/TrackMate
Merge branch 'master' of ssh://github.com/fiji/TrackMate
Merge branch 'master' of ssh://github.com/fiji/TrackMate
Merge branch 'master' of ssh://github.com/fiji/TrackMate