Introduce use of override keyword for virtual methods; added corresponding gcc warning.

CMakeLists.txt

include/tsid/contacts/contact-6d.hpp

include/tsid/contacts/contact-base.hpp

include/tsid/contacts/contact-point.hpp

include/tsid/contacts/contact-two-frame-positions.hpp

include/tsid/contacts/measured-3d-force.hpp

include/tsid/contacts/measured-6d-wrench.hpp

include/tsid/contacts/measured-force-base.hpp

...d/formulations/inverse-dynamics-formulation-acc-force.hpp

...e/tsid/formulations/inverse-dynamics-formulation-base.hpp

include/tsid/math/constraint-base.hpp

include/tsid/math/constraint-bound.hpp

include/tsid/math/constraint-equality.hpp

include/tsid/math/constraint-inequality.hpp

include/tsid/robots/robot-wrapper.hpp

include/tsid/solvers/solver-HQP-base.hpp

include/tsid/solvers/solver-HQP-eiquadprog-fast.hpp

include/tsid/solvers/solver-HQP-eiquadprog-rt.hpp

include/tsid/solvers/solver-HQP-eiquadprog.hpp

include/tsid/solvers/solver-HQP-qpmad.hpp