Adds given **Active_QLabel** Widget.

        :param active_label: Active label to add.
        :type active_label: Active_QLabel
        :return: Method success.
        :rtype: bool

def add_active_label(self, active_label):
        """
        Adds given **Active_QLabel** Widget.

        :param active_label: Active label to add.
        :type active_label: Active_QLabel
        :return: Method success.
        :rtype: bool
        """

        if not issubclass(active_label.__class__, Active_QLabel):
            raise foundations.exceptions.ProgrammingError("{0} | '{1}' must be a '{2}' subclass!".format(
                self.__class__.__name__, active_label, Active_QLabel.__name__))

        if active_label in self.__active_labels:
            raise foundations.exceptions.ProgrammingError("{0} | '{1}' is already in the collection!".format(
                self.__class__.__name__, active_label))

        active_label.checkable = True
        not self.__active_labels and active_label.set_checked(True) or active_label.set_checked(False)
        self.__active_labels.append(active_label)

        # Signals / Slots.
        active_label.toggled.connect(functools.partial(self.__active_label__toggled, active_label))

        active_label.clicked.connect(functools.partial(self.active_label_clicked.emit, active_label))
        active_label.pressed.connect(functools.partial(self.active_label_pressed.emit, active_label))
        active_label.released.connect(functools.partial(self.active_label_released.emit, active_label))
        active_label.toggled.connect(functools.partial(self.active_label_toggled.emit, active_label))

        return True