Begin the implementation of a multicontact PG based on Hirukawa2007

Adding oder 7 polynome to be used to compute X,Y,Theta position for the feet.
Do a little cleanup of the computation of the foot position.

Not all structures (especially private ones) have an ostream operator because I
did not need them this time, not for any technical reason

(one useful commit...)

This reverts commit 3e994c89.

This reverts commit 2edb055d.

This reverts commit 1e8102d9.

More specifically take into account the new headers of
abstract-robot-dynamics.