inception_cmake: CMake Tensorflow Serving Client

These are my hacks around getting a Tensorflow Serving client (using the tutorial inception_client.cc) in C++ built via CMake. There's a few changes in the CMake submodules to let me invoke the protobuf compiler to support the *.proto file layout that exists in the tensorflow/serving repository. This checks out the serving submodule to the official repository and moves the CMakeLists.txt file out. This assumes the following have been installed:

1. Protobuf (I'm using libprotoc 3.4.0)
2. gRPC (I'm using libgrpc.so.5.0.0)
3. Tensorflow installed via tensorflow_cc. I used TensorflowCC::Shared but TensorflowCC::Static should also work for this example

Build

If this is the first time, make sure to fetch the submodule files

git submodule update --init --recursive

mkdir build && cd build
cmake ..
make