TEHRAN, July 20 (Reuters) - Germany and Iran moved tentatively on Monday towards reviving a once close trade relationship, anticipating the lifting of western economic sanctions against Tehran following a landmark nuclear deal. Economy Minister Sigmar Gabriel, making the first top level German government visit to Tehran in 13 years, indicated that a ministerial-level meeting of a long dormant German-Iran economic commission would take place early next year in Tehran. Gabriel signalled the move at a meeting with Iranian Oil Minister Bijan Namdar Zangeneh during the visit, which is also the first to the country by a senior member of...