1.Re-implement RelativePositionConstraint using quaternions in MATLAB
2.Change some quaternions functions for faster speed.
3.Start to write RelativePOsitionConstraint in C++
1. Implement C++ RelativePositionConstraint
2. Add a method evalNames to PositionConstraint, so now the logic is cleaner. The non-abstract class in PositionConstraint only needs to take care of all the position name, and do not need to worry which position is actually included in the final constraint
Now RelativePositionConstraint is fully supported in C++