fixes #348 - added ability to define drilldown action with F key.
NOTE: need to create a custom class, and use it, in
@ScreenNavigation.action e.g:

public class F8DrilldownAction extends F8 implements
TerminalDrilldownAction {

	private static final long serialVersionUID = 1L;

	private Object actionValue;

	public F8DrilldownAction() {}

	@Override
	public Object getActionValue() {
		return actionValue;
	}

	@Override
	public void setActionValue(Object actionValue) {
		this.actionValue = actionValue;
	}
}