JAKARTA, Indonesia — Joko Widodo, a commoner who was born in a Javan slum, was sworn in Monday as president of Indonesia, completing an improbable rise from hometown mayor to leader of the world’s fourth most-populous nation. With a Quran held above his head, Widodo took the oath of office during a nationally televised special session of the People’s Consultative Assembly, a legislative superbody dominated by the House of Representatives.