* Ahead of Davos meeting, forum warns of "lost" generation
* Widening wealth gap ranked as top global risk in 2014
* Extreme weather next most likely cause of major shocks
* Threat of fiscal crises significant, but danger receding
By Ben Hirschler
LONDON, Jan 16 (Reuters) - A chronic gap between rich and poor is yawning wider, posing the biggest single risk to the world in 2014, ...