Before, app crash on some machines as been reported in #15 and #16, and cannot easily be reproduced on other machines, such as a virtual box guest system, which make it very hard to trace the root cause.
Now, the offline render is totally removed from the code base, instead of offline-render to image then show the image, we can directly show the parts model in the parts tree using normal opengl widget, and the result looks better than before.
This feature could be useful for smooth one component and soften the seam of combination,
This commit also include a crash fix about incorrect use of CGAL.
Jeremy Hu