Added external build of the nlopt library
Added external nlopt cmake file for that for external build of nlopt library
Slicer cannot load module when it is linked statically to nlopt lib. Removed the library for now... Should try to create a shared library instead.
Add in-plane rotation and translation for plane fitting (after RANSAC), using simple geometrical rules. For the in plane rotation we preserve angles with the 2 inplane axis. For the translation we preserve the centroid of the point sets.