Currently for most of the problems we look at, loops (an edge going into
the same state) are not useful. However, these loops appear in a lot of
state sequences considered by the algorithm and slow it down
significantly. Until we encounter a problem where loops are necessary to
accomplish the task, we should just ignore them.

fix submodule url

  - Use parent implementation for method solve,
  - reimplement tryToConnectInitAndGoals,
  - remove InStatePath class and call core::DiffusingPlanner instead.
  - optimize paths on sub-manifolds with random shortcut and insert path
    in roadmap.

  when calling a path planner in hpp-core.
  Throw core::path_planning_failed when interrupted.

Fix steeringMethod::CrossStateOptimization

  - do not copy constraints from graph solvers,
  - in solver construction, use target constraints of transitions instead of
    merging solvers of edge, graph and target state. In target constraints,
    constraints and complements are merged when necessary.

  Do not clear constraintsAndComplements_ after graph initialization,
  Add method clearConstraintsAndComplement(),
  call this method in ProblemSolver::initConstraintGraph().

  - add parameter "CrossStateOptimization/nRandomConfig" to specify the number
    of trials to generate each waypoint configuration.

  if starting configuration slightly violates the constraint.
  Return false instead.

This reverts commit 0d81bac3.

  - only before initialization.

  - remove duplicate loop.

  - GraphComponent::numericalConstraints is virtual,
  - reimplemented in Edge a follows:
    - if edge is not initialized, call parent implementation,
    - otherwise return constraints that are in the solver.
  - The differences are that:
    1. constraints and complements are replaced by explicit constraints,
    2. constraints of the containing node are also returned.

  - Methods of class Implicit that use member rhs_ have been made deprecated.

  - when inserting them. Throw if they are.
  - Add a test.

  to comply with modification in hpp-constraints.

  This fixes a bug due to numerical approximation. In some cases, an explicit
  constraint of the path is satisfied for a configuration, but the constraint
  of the node that is supposed to contain the path constraint is not satisfied.

  RelativeTransformation -> RelativeTransformationSE3 with mask.