Fix signal interface generation

[poeschel]

Interface generation for signals is wrong in some way. This simple signal

`

`

using InterfaceCodeGenerator generates to this interface ` public interface Example extends DBusInterface { public static class ExampleSignal extends DBusSignal {

        private final String newState;

        public ExampleSignal(String _path, String _interfaceName, String _newState) throws DBusException {
            super(_path, _interfaceName);
            this.newState = _newState;
        }

        public String getNewState() {
            return newState;
        }
    }
}

`

which is wrong. The constructor should be like this instead: public ExampleSignal(String _path, String _newState) throws DBusException { super(_path, _newState); this.newState = _newState; }

Explained a bit more in the commit message.