move bert demo to examples namespace

[brettkoonce]

fixes import warnings, eg "'TensorFlowModels' /home/skoonce/swift-models: warning: ignoring duplicate product 'TextModels'"

[saeta]

Thank you very much @brettkoonce ! This is really great.

[BradLarson]

I think we may have collided here, because I did the same with PR #321 that I just submitted. I had been working on a larger reorganization of the model so that the dataset and an example like the above could be extracted. I made a few more elaborate changes to the overall structure as a first step so that we can remove some duplicate code and reuse some of this in the Transformer example.

I liked your phrasing better in your Readme, so I used that for the text in the BERT-CoLA Readme I submitted as part of my pull request. Thanks for writing that up.

Sorry for not making it clear that I was working on this. If you'd prefer to have your PR landed first, I think I can rework mine to be a follow-on to yours.

[brettkoonce]

nbd, carry on!

[BradLarson]

Thanks, again sorry about that. Appreciate the cleanup work.