Interactive cli for python converter

[pyu10055]

It is a command tool that guides the user through the converter options. Here is an updated video for the cli.

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[nsthorat]

Ping, amazing work! This is incredible. Few high level points:

• I wonder if we should have this in a small design doc because it would give more people an opportunity to look at this (a lot of people have used the converter now!)
• Some of the things it would be great to do automatically! Like can we detect the input format and print "We found a TensorFlow SavedModel!"
• It's unclear what "tags" are, can we automatically print them all?
• What is a signature? Can we print that too?
• When you ask about compression it would be great to show the options with details (e.g. "1) 4x compression, highest accuracy loss 2) 2x compression, some accuracy loss)
• It would be good to give a little explainer for each of the questions, e.g. What is op validation? What does stripping debug ops do?

[nsthorat]

Let's talk over there! I think we still should detect the input format :)

[caisq]

@pyu10055 It just occurred to me, but you might want to verify that PyInquirer works in notebook environments such as Jupyter Notebook and CoLab. From our experience, we know many of our users do their Python model training and subsequent conversion in notebooks. It would not be ideal if the interactive CLI doesn't work in those environments.