Implementation of one way collisions for chain and edge shapes

Updated code based on pull request #236 which uses the ContactFilter to avoid modifying the Box2D library. Currently chain and edge shapes need to be offset from the center of the scene object for the one way property to work. Thanks to @RichardRanft for the original submission.

Forum discussion can be found here: http://www.garagegames.com/community/forums/viewthread/138755