Added check to ensure the Learner returnCode is OK. (NVIDIA#108)

* Added check to ensure the Learner returnCode is OK.

* Fixed black reformat.

* Changed to check the from_shareable() explictly.

* Added from_shareable(validate_result) in the try block.

Fixed the args.log_config setting. (NVIDIA#86)

* Fixed the args.log_config setting.

* Enhanced to allow FL app config/log.config to overwrite the settings.

Fix TensorBoard streaming app test's result validator (NVIDIA#77)

fix documentation image not loading (NVIDIA#28)

Cleanup examples (NVIDIA#9)

Merge pull request NVIDIA#1 from NVIDIA/ready

Initial commit for 2.0