Enable multi-session CD/DVD-burning by default

The default cd burning application of Ubuntu (nautilus-cd-burner) has one major deficiency: The lack of multi-session support. In order to save money and the environment, one should not be forced to use a new medium for evey burning process, even if 90% of the disk are still free. So the cd burning application should have multisession support enabled by default.

In order to implement this, either nautilus should be extended by this longly awaited feature, or another burning application should become Ubuntu's default. Brasero for example provides a simple and clean user interface and has support for this.