Add extra selections to DecorationsManager.

        TODO: This method could be remove it and decorations could be
        added/removed in set_extra_selections/clear_extra_selections.

def update_extra_selections(self):
        """Add extra selections to DecorationsManager.

        TODO: This method could be remove it and decorations could be
        added/removed in set_extra_selections/clear_extra_selections.
        """
        extra_selections = []

        for key, extra in list(self.extra_selections_dict.items()):
            extra_selections.extend(extra)
        self.decorations.add(extra_selections)