TF .pb wont save in Colab local

To save in Colab, we need to add some lines if we train with TPU because it usually requires to be saved to a Bucket. To overcome the use of a Bucket, add the `SaveOptions` as follows to the `fit() `function:

```
if export_model:
save_locally = tf.saved_model.SaveOptions(experimental_io_device='/job:localhost')
self.model.save(export_model, options=save_locally)
print('Model exported')
```

Review the training code around the fit() function and its export_model path, then inspect linked pull request #30 for the work already underway. Verify the requested SaveOptions behavior in a Colab TPU run; done means a .pb SavedModel is written locally without requiring a bucket.

Written by the indexing model from the issue text.