SkeletonState now saves the entire skeleton state.

Since with IKSolver the chain can be any size it is necesary for SkeletonState
to save/restore the current state of all the bones.
SkeletonFitting added method knn_division_done

This method checks if the current leg division is correct.
recalculate_right_left_knn now recalculates everything until
knn_division_done returns true.
SkeletonFitting when fit leg fails it now tries with a simpler fit.

All fitting methods now have a return value, true for a successfuly fit and
false otherwise