* Enable running PEP8 checks via flake8 as part of the build if flake8 is installed.
Update scripts in \tools and \onnxruntime\python. Excluding \onnxruntime\python\tools which needs a lot more work to be PEP8 compliant. Also excluding orttraining\tools for the same reason.
Install flake8 as part of the static_analysis build task in the Win-CPU CI so the checks are run in one CI build.
Update coding standards doc.
Update ReformatSourcePython.bat to use YAPF to format python code, and add onnxruntime\test directory to be formatted.
Add onnxruntime\.style.yapf for configuration. The style is based on google, except max column width 120.
Format python scripts using ReformatSourcePython.bat.
* py fallback initial commit.
* fixes.
* update NGRAPHCustomOp::Initialize() to return Status
* fixes in session.py
* FAIL status to EP_FAIL in ngraph custom op
* disable fallback for backend api
