use sole frame instead of last joint + transform
Created by: pFernbach
Main change : now use the leg_***_sole_fix_joint
as the center of contact instead of leg_****_6_joint
with a transform. This doesn't change anything in the scripts using this class.
Other change :
- Increase the vertical size (toward the ground) of the trunk_large bounding box
- Reduce the root z value of the references configuration to be in contact (without collisions) with a floor at z = 0