Re-introduce GPU parallel Jacobi solver, called btGpuJacobiContactSolver. There are still some issues, but for basic scene's it works.

To avoid confusion, rename GPU contact solver to btGpuContactSolver, and constraint (non-contact) solver to btPgsConstraintSolver.

Demos3/GpuDemos/main_opengl3core.cpp

@@ -84,7 +84,7 @@ enum
 };
 
 b3AlignedObjectArray<const char*> demoNames;
-int selectedDemo = 1;
+int selectedDemo = 0;
 GpuDemo::CreateFunc* allDemos[]=
 {
 		//ConcaveCompound2Scene::MyCreateFunc,