Added polysIntersect() which tests the polys' BBs overlap before bothering to do the intersection.
Added polysIntersect() which tests the polys' BBs overlap before bothering to do the intersection.

Ultimaker/CuraEngine,ROBO3D/CuraEngine,Ultimaker/CuraEngine,alephobjects/CuraEngine,alephobjects/CuraEngine,alephobjects/CuraEngine,ROBO3D/CuraEngine,ROBO3D/CuraEngine