Parallelized collision detection

Written for woo by Václav Šmilauer on 2014-08-19

InsertionSortCollider is now parallelized using partial sorts, for both aperiodic (since rev. 3529) and periodic (since rev. 3551) boundaries. The speedup is massive, e.g. 5x faster simulations for 120k particles. Thanks to Bruno Chareyre from Yade for the idea.