Changes based on discussions in the work group

1) Skeleton structure was simplified (omitting fingers, eyes, and jaw); FULL_HAND introduced instead;
2) Coordinate reference was redefined with bbcenter_to_root;
3) Skeleton Point was renamed to Bone for clarity;
4) Length attribute added to the bone;

Signed-off-by: Jakob Peintner <jakob.peintner@thi.de>

Author: Peintnerer