embed TCP graphics server in PyBullet for easier working-from-home

This allows to render at a different machine, sending all assets across the TCP network, using port 6667 by default.
You can use ssh port forwarding to get this working:
ssh -R 6667:localhost:6667 username@remotehost.com -v

python3 -m pybullet_utils.graphicsServer
python3 -m pybullet_utils.graphicsClient

Note that there are still some tcp networking issues that can cause a hang, just restart graphics server and graphics client if it hangs.

examples/SharedMemory/RemoteGUIHelper.cpp

@@ -218,6 +218,11 @@ RemoteGUIHelper::~RemoteGUIHelper()
 	delete m_data;
 }
 
+bool RemoteGUIHelper::isConnected() const
+{
+	return m_data->isConnected();
+}
+
 void RemoteGUIHelper::setVisualizerFlag(int flag, int enable)
 {
 	GraphicsSharedMemoryCommand* cmd = m_data->getAvailableSharedMemoryCommand();