Move PointXYZLAB to common?

[mvieth]

The point type PointXYZLAB is currently defined in gicp6d. The definition could be moved to point_types.h and point_types.hpp, and conversions could be moved from gicp6d.cpp to point_types_conversion.h

Pros:

• Types like PointXYZRGB(A) and PointXYZHSV are in point_types
• Currently doxygen seems to be confused by the macros in gicpd6d.h (see here under Function Documentation), that would be solved by moving the definitions

Cons:

• Currently PointXYZLAB is only used by GeneralizedIterativeClosestPoint6D

[kunaltyagi]

Not against the proposal, and the cons is not that big of an issue (IETF style)