Const correctness and documentation

src/Mathematics/FootConstraintsAsLinearSystemForVelRef.cpp

src/Mathematics/FootConstraintsAsLinearSystemForVelRef.h

src/Mathematics/intermediate-qp-matrices.hh

src/PreviewControl/SupportFSM.cpp

src/PreviewControl/SupportFSM.h

src/ZMPRefTrajectoryGeneration/ZMPVelocityReferencedQP.cpp

src/ZMPRefTrajectoryGeneration/generator-vel-ref.cpp

src/ZMPRefTrajectoryGeneration/generator-vel-ref.hh