Release v0.12.0.

- Disabled loading of Views states. It proves to bring confusion and
  bugs.
- Add a 3rd panel containing MaMuT specific actions.
- Add an action to merge current annotation with the annotation coming
  from another file. Right now, it does not check whether the same cell
  is present in the two annotations.
- Add an action to extract the 2D or 3D stack following a specific cell
  lineage.
- Allow backward lineaging in auto-llinking mode.

Acquaint recent changes in BDV and TrackMate
- The color range for feature display can be set manually.
- In TrackScheme info pane, resize columns to always display the full
  name of spots.

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