Release v2.5.0.

- A full rewrite of the LAP (simple and not simple) tracker, that takes
  advantage of the sparse structure of tracking problems. This has major
  consequences on the memory usage and on speed performance. Because the
  results are not strictly identical, the old version of the LAP tracker
  is still present.

- TrackScheme has now a search box that will center the view on the
  spots with names that match.

- TrackScheme main panel has proper row and column headers that stay
  visible even when scrolling away from the border.

- A new action that examplify a branch-based analysis.

- Minor usability tweaks.

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