Add placeholder for the projects default package name

In a feature for a training I add a class org.example.channel.MyChannelInfo. I want to refer to that class in an xml file that will be injected in the project. The "org.example" bit is dependent on the package name that was choosen when the project was created with the archetype. There is no placeholder yet for this. There is

{{beansPackage}}

and

{{componentsPackage}}

. I think we also need

{{projectPackage}}

that contains "org.example" or whatever package was choosen.