Allow to solve constraints level by level.

  "Graph-SteeringMethodStraight" and "Graph-Straight" refer to the same
  steering method.

  when robot contact surfaces are not on a freeflying object.

Fix bug in code for mask

These errors are shown when compiled in debug mode.

Change license to BSD 2 clauses.

[Handle] Allow to customize mask complement.

[GraphValidation] Add method to get collision list for a node

fix submodule url

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.