Octree-based Collision Detection

Using Octree to detect collision between geometries.

• Implement OctreeBasedCD class for detecting collisions between meshes
• Write multiple collision test examples
• Write unit test for Mesh-Mesh CD
• Write unit test for PointSet-Mesh CD
• Write unit test for PointSet-Analytical Geometry
• Clean-up and squash commits to merge
• Add an octree as a static member of CollisionDetection class, allowing to share it to detect collision in the derived classes
• Implement PointSet-Mesh collision detection using Octree
• Implement Mesh-Mesh collision detection using Octree
• Add unit tests for PointSet-Mesh and Mesh-Mesh collision detections

Note: The current PBD system is very inefficient and must be improved in future. Having collision data, resolving collisions between PBD objects is still very slow and unstable.