Tag Ristretto 0.5.0

- Use only one toolbar
- Remove the 'close' button from the toolbar, and replace it
  with an 'edit' quick-launcher.
- Add support for a default editor.
- Replace the thumbnailbar with a port of exo-icon-bar
- Remove exo dependency
- Support http://docs.xfce.org/ for documentation
This tag has no release notes.