Enable a NApp if not already enabled.

        Raises:
            FileNotFoundError: If NApp is not installed.
            PermissionError: No filesystem permission to enable NApp.

def enable(self):
        """Enable a NApp if not already enabled.

        Raises:
            FileNotFoundError: If NApp is not installed.
            PermissionError: No filesystem permission to enable NApp.

        """
        core_napps_manager = CoreNAppsManager(base_path=self._enabled)
        core_napps_manager.enable(self.user, self.napp)