OpenCL GPU rigidbody pipeline

[Stefan]

OpenCL_gpu_rigidbody_pipeline_AMD is a proof of concept of a rigid body simulation, entirely running on GPU using OpenCL.
The demo currently only runs on AMD Radeon with up-to-date graphics/OpenCL drivers. It works on a recent NVIDIA GPU with
latest 290.53 graphics drivers.
The OpenCL kernels are compiled the first time you run the demo. After that, the startup time should be much better.