IKSolver improved methods to initialize chain with an offset

This methods are still not working.
Cloudclusterer fix uninitialised variable.

body_height_extra_threshold was being used without initialisation.
Not even sure how could it work before.
Skeleton fitting, improved leg fitting.

Now when a method fails it leaves the leg as it was before it tried to fit it.
MocapData moved header initialisation to MocapHeader

The header initialisation should be in the header class.
SkeletonFitting improved method fit_leg_position_go_up_y.

Loop is more simple and calculated positions are new always of the appropiate
bone length.
SkeletonFitting fit_leg_position_go_up_y improved

The method now reliably puts the three first bones of each leg when it works.
Before the second bone would sometimes be in a wrong position.
SkeletonController user can now modify fitted skeleton.

Before it was either fitting or user modifing the skeleton, now it first fitts
and then lets the user modify. Once modify there is no way to tell it to do the
fitting again