Replace createStaticStabilityConstraint by addStaticStabilityConstraint,

  - pass config projector instead of creating a new one,
  - do not specify errorThreshod and maxIterations, they are stored in
    ConfigProjector.
Replace addSlidingStabilityConstraint by createSlidingStabilityConstraint

  - return a vector of DifferentiableFunctionPtr_t pointers.
Update to modification of constraint definitions in hpp-constraints.