Merge branch 'belenos' into 'belenos'

A session to use unity has been added

Sadly, there is no session files in the package to make unity be listed by the login manager. This should solve the problem.

It is mandatory that the session and desktop files are named "ubuntu.<suffix>" to make the whole thing work but one can change the name that will be displayed by the login manager.

I've tested most things and no problems have been found with this.

See merge request !116