Update reference to soth (point towards github not laas).

Pointed out by Aurelie Clodic.
Added Relative MetaTaskDyn and modified CMakeLists
Added gain utilisation to task-dyn-limits.cpp and  added some useful comments
Added secondOrderKinematics option with drift Jdot*dq compensation in solver-kine and userfriendly changes/commentaries in solver-op-space.cpp
Added control on task type when second order is set