[BUG] createGLBuffer and copyToGLBuffer do not point to the same device

If you have more than one display cards, all the examples in forge/examples/opencl will fail.

A temporary workaround is to modify createCLGLContext in cl_helpers.h so that cl::Context always use the last device instead of the first device. But it is not a solution at all.

```
void get_devices(const forge::Window &wnd,
std::vector &platforms_interop,
std::vector &devices_interop) {
std::vector platforms;
Platform::get(&platforms);

for (auto platform : platforms) {
std::vector devices;
try {
platform.getDevices(CL_DEVICE_TYPE_GPU, &devices);
for (auto device : devices) {
if (checkGLInterop(platform, device, wnd)) {
devices_interop.push_back(device);
platforms_interop.push_back(platform);
}
}

} catch (const cl::Error &err) {
if (err.err() != CL_DEVICE_NOT_FOUND) {
std::cout << "Platform: " << platform.getInfo()
<< " got error = " << err.err() << std::endl;
throw std::runtime_error("Fatal Error!");
}
}
}
if (devices_interop.size() == 0)
throw std::runtime_error("No CL-GL sharing contexts found");
}

cl::Context createCLGLContext(const forge::Window &wnd, cl::Platform platform,
cl::Device device) {
// std::cout << "Platform: " << platform.getInfo()
// << std::endl;
// std::cout << "Device: " << device.getInfo() << std::endl;
#if defined(OS_MAC)
CGLContextObj cgl_current_ctx = CGLGetCurrentContext();
CGLShareGroupObj cgl_share_group = CGLGetShareGroup(cgl_current_ctx);

cl_context_properties cps[] = {CL_CONTEXT_PROPERTY_USE_CGL_SHAREGROUP_APPLE,
(cl_context_properties)cgl_share_group, 0};
#elif defined(OS_LNX)
cl_context_properties cps[] = {CL_GL_CONTEXT_KHR,
(cl_context_properties)wnd.context(),
CL_GLX_DISPLAY_KHR,
(cl_context_properties)wnd.display(),
CL_CONTEXT_PLATFORM,
(cl_context_properties)platform(),
0};
#else /* OS_WIN */
cl_context_properties cps[] = {CL_GL_CONTEXT_KHR,
(cl_context_properties)wnd.context(),
CL_WGL_HDC_KHR,
(cl_context_properties)wnd.display(),
CL_CONTEXT_PLATFORM,
(cl_context_properties)platform(),
0};
#endif
return cl::Context(device, cps);
}

cl::Context createCLGLContext(const forge::Window &wnd) {
std::vector platforms;
std::vector devices;
get_devices(wnd, platforms, devices);
for (size_t i = devices.size() - 1; i >= 0; i--) {
// for (size_t i = 0; i < devices.size(); i++) {
try {
return createCLGLContext(wnd, platforms[i], devices[i]);

} catch (const cl::Error &err) {
std::cout << "[createCLGLContext]Error:" << err.err() << std::endl;
}
}
return cl::Context();
}
```