Create a set of helper classes to create ceres optimisation problems on splines

[cedricpradalier]

This PR is a proposal of a set of tools that will help creating optimisation problems with Ceres and splines of Sophus objects, dealing with all the special cases of knot selection at the beginning and at the end of the knot vector, as well as the derivative

A functor can be optimized on the spline knots with a code as simple as:
`std::shared_ptr spline(new Splined(control_poses, -1.0, dt)));
ceres::Problem problem;

auto parametrization = new Sophus::Manifold<LieGroup_>;
for (auto v : spline->parent_Ts_control_point()) {
  problem.AddParameterBlock(v.data(), LieGroupd::num_parameters, parametrization);
}

for (size_t i = 0; i < group_vec.size(); ++i) {
    double t = i;
    std::shared_ptr<Functor> functor(new Functor(group_vec[i]));
    SES::template addResidualFunction0<Functor,DoF>(problem,t,spline,functor);
  }

`
addResidualFunctions are provided for functor taking one or two points on the spline, or its first and second derivative, as well as functor depending on one or two other objects (for instance extrinsic or intrinsic calibrations).

Adding the KnotAndU class is critical to this code to easily recover the knots and u value corresponding to a specific time stamp.

I hope that can be useful. I find that these structures are strongly simplifying my writing.