Build a cached dict with settings.INSTALLED_APPS as keys
        and the 'templates' directory of each application as values.

def app_templates_dirs(self):
        """
        Build a cached dict with settings.INSTALLED_APPS as keys
        and the 'templates' directory of each application as values.
        """
        app_templates_dirs = OrderedDict()
        for app_config in apps.get_app_configs():
            templates_dir = os.path.join(
                getattr(app_config, 'path', '/'), 'templates')
            if os.path.isdir(templates_dir):
                templates_dir = upath(templates_dir)
                app_templates_dirs[app_config.name] = templates_dir
                app_templates_dirs[app_config.label] = templates_dir
        return app_templates_dirs