Add a mask in construction of relative transform constraint.
Add a mask to RelativePosision and RelativeTransformation constraints

  - mask is a vector of boolean values defining which  coordinate of the
    error vector needs to be regulated to 0.
Fix bug in error and Jacobian computations.

  Dispatch to position and orientation constraints depends on mask.
Merge branch 'master' of https://github.com/humanoid-path-planner/hpp-constraints