Initialize for object detection example

[polltooh]

In this tutorial, it includes a IPython notebook for building, training and testing an object detection model end to end. Also it includes object_detection_lib, which contains all the necessary utility functions for running the notebook.

[lamberta]

Thanks, Geoffrey.

This was originally tensorflow/docs#238 but would fit better in the examples repo.

@wolffg is working to organize this repo so PTAL.

[MarkDaoust]

This is an important example, I'll fixup any outstanding issues and get it merged.