Xar plugin should not embed anything by default

That's against maven logic, embedding dependencies should always be used for final distributions in project containing pretty much nothing except dependencies.

For example it's an issue with Extension Manager since if you require some other xar (with some class for example) as dependency of your xar, your only choice is either to embed it and make impossible to update one without the other or not declare it as a dependency and take the risk that your application does not work if your dependencies have not been already installed.