* ADF-NALU group based in eastern Congo since mid 2000s
* Congolese army launched offensive in December
* Mukulu has been helped to reach another country
By Elias Biryabarema
KAMPALA, April 22 (Reuters) - The leader of a Ugandan Islamist rebel group has fled his hideout in eastern Democratic Republic of Congo after a U.N.-backed offensive destroyed several camps belonging to his militia...