Release v2.5.1.

    - Fix several issues with the manual tracking plugin. Files were saved with
    missing information, generating warnings upon reloading.

    - Fix a bug with the semi-automatic tracker, not putting the correct time
    feature to found spot.

    - The GUI is resizable, so as to avoid bad suprise when using TrackMate
    on several different OSes.

    - Format the display of floating point numbers in a better way.

    - Tweak the toolbar of TrackScheme.

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