- refactoring of constraints.

  - use constraints::implicit::RelativePose and
    constraints::explicit_::RelativePose.

    core::NumericalConstraints -> constraints::Implicit
    core::Equation -> constraint::explicit
    core::ExplicitNumericalConstraints -> constraint::explicit
    core::LockedJoint -> constraints::LockedJoint

    Replace a few remaining deprecated symbols.

    core::NumericalConstraints -> constraints::Implicit
    core::Equation -> constraint::explicit
    core::ExplicitNumericalConstraints -> constraint::explicit
    core::LockedJoint -> constraints::LockedJoint

    hpp::constraints::HierarchicalIterativeSolver ->
      hpp::constraints::solver::HierarchicalIterative,
    hpp::constraints::HybridSolver -> hpp::constraints::solver::BySubstitution
    hpp::constraints::ExplicitSolver -> hpp::constraints::ExplicitConstraintSet

  - when building edges by hand, this assert may fail eventhough the problem
    is well posed.

  - assert that if not equal, distance between 2 successive configuration is
    more than 1e-8.
  - this complies with hpp-core policy acording to which, a constraint does
    not modify a configuration if the configuration satisfies the constraint.

  - copy paste and adapt code of hpp::core::ConnectedComponent.

  - RoadmapNode::symbolicComponent -> RoadmapNode::leafConnectedComponent,
  - Roadmap::symbolicComponents -> Roadmap::leafConnectedComponents.
  - rename private member Roadmap::symbolicCCs_ -> leafCCs_,
  - rename private member RoadmapNode::symbolicCC_ -> leafCC_.