Use the pr2 with the sot.

This code has been validated on the real pr2 robot, for arm motions, while the motion of the base have only been tested in kinematic simulation.
The groovy branch will follow, as soon as this PR is validated.

There are still several possible improvements to be made (removal of some of the joints, e.g. the wheels),
but I think that this current version is mature enough to be in the main branch repository.

Note: for now, the travis only warns me. I will replace it by the hpp mailing list as soon as this PR is accepted.