Bnd plugin for karaf commands

Karaf 4 commands are identified by the annotation
org.apache.karaf.shell.api.action.lifecycle.Service

For performance reasons karaf only processes commands in packages listed in the Manifest property:
Karaf-Commands:

We could spare people from adding the header above by hand by creating a small bnd plugin that scans for the above annotations and adds the header.

I can provide a pull request for this.