LONDON, March 14 (Reuters) - Over 90% of its residents have fled, much of it lies in ruins, tens of thousands have been killed, and its strategic importance has been played down by the Pentagon and NATO chiefs. Yet Russia and Ukraine are still battling for the small city of Bakhmut. After nearly eight months of trench warfare Ukrainian forces are surrounded on three sides, Kyiv's supply lines are fraying, and Moscow is in control of just under half of Bakhmut. Still, Ukraine has pledged to double down on the city's defence even as both sides take heavy casualties. Some...