UE3 animation support

I was implemented animation support for UE3 meshes (AnimSet object) in Unreal Model Viewer. To view animations in umodel AnimSet and SkeletalMesh should be loaded together (currently it is possible when they reside in the same package). To bind AnimSet to mesh press Ctrl+A key in viewer (this will cycle between all loaded AnimSets). Tested with Unreal Tournament 3 and Gears of War.