Europe's worst drought in years has pushed the mighty river Danube to one of its lowest levels in almost a century, exposing the hulks of dozens of explosives-laden German warships sunk during World War Two near Serbia's river port town of Prahovo.The vessels were among hundreds scuttled along the Danube by Nazi Germany's Black Sea fleet in 1944 as they retreated from advancing Soviet forces, and still hamper river traffic during low water levels.However, this year's drought…