actual version of DDP always compute a command trajectory finishing by a null command
it is a problem for the pneumatic actuator model using QPBox
this fix is temporary and will require more deep modifications of the DDP

in this case, thge solver doesn't use the 2nd order derivatives of the dynamics

previously QPBox only worked for single command system

[minor]new executable fo test QPBox

[minor]several modifications on class handle

This reverts commit 83f2990f.

the use of x and xDes was creating a computation problem
It is now necessary to use only x = xCurrent-xDes in DDP

Qt tmp