modify vgg16 cats/dogs example on Colab to include fetching data from google drive

[srodney]

currently the user has to manually pull the data from Kaggle, and since colab data storage is not persistent, it has to be fetched fresh each time.

Better solution would be to set up the python script to grab it from google drive and organize it locally each time.

[srodney]

resolved with commit 6215da9

Now fetches data automatically from a public Google drive link using !gdrive

Also adopted the updated model definition and test harness from @AdkPete - so the colab notebook here is largely redundant with Pete's python module here