WIP: ONNX Runtime Example, master branch (2020.03.16.)

This MR is supposed to give @dbakshig some help with his efforts on creating this example. I've taken the code that he wrote in !30886 (closed), and put a somewhat cleaner algorithm and service on top of it. Ones that use the C++ API of ONNX Runtime.

Note that the example algorithm (AthONNX::CxxApiAlgorithm) only loads a model from the calibration area, and prints some information about it. It doesn't send any data through the model. I'd let Debo figure out that part of the code...

This is also supposed to give some best practices for the CMake configuration of the package. 😉