command-to-code package for Weka 3.9.0+

Earlier this year, Weka’s GUIChooser code got refactored and moved out to weka.gui.GUIChooserApp. Unfortunately, this seems to have broken the old main menu extension. Therefore I decided to use the new way of adding menu items for the command-to-code-weka-package, implementing weka.gui.GUIChooser.GUIChooserMenuPlugin instead. While doing this, I also switched the minimum requirement for Weka to be 3.9.0.

In a nutshell, a new release is out: 2016.5.8