Soft delete object (set its ``is_removed`` field to True).
        Actually delete object if setting ``soft`` to False.

def delete(self, using=None, soft=True, *args, **kwargs):
        """
        Soft delete object (set its ``is_removed`` field to True).
        Actually delete object if setting ``soft`` to False.
        """
        if soft:
            self.is_removed = True
            self.save(using=using)
        else:
            return super(SoftDeletableModel, self).delete(using=using, *args, **kwargs)