make PhysicsClient an interface class, and move shared memory implementation

of physics client into PhysicsClientSharedMemory class/file.
This will allow implementation of UDP and other transport protocols to a physics server.

examples/ExampleBrowser/CMakeLists.txt

@@ -16,6 +16,7 @@ SET(App_ExampleBrowser_SRCS
 	ExampleEntries.cpp
 	ExampleEntries.h
 	../SharedMemory/PhysicsServer.cpp
+	../SharedMemory/PhysicsClientSharedMemory.cpp
 	../SharedMemory/PhysicsClient.cpp
 	../SharedMemory/PhysicsClientC_API.cpp
 	../SharedMemory/PhysicsServerExample.cpp