Refactor Jupyter file for protein structure alignment example

[FanwangM]

This PR refactors protein structure alignment example with Procrustes.rotational. Main changes are

• [x] Update figure with the subfigure from the manuscript
• [x] Try to simplify the descriptions
• [x] Add the corresponding folder for this example.

Some other points not address in this PR,

• [ ] We will delete all the contents in the examples folder in the docs directory, but let's leave it after all the changes on Jupyter notebooks have been merged.
• [x] One more point is that we need to update the figure title, both in the manuscript and this Jupyter notebook as we are using rotational Procrustes module, not the orthogonal one.
• [x] We may also need to use a lower resolution figure as this one takes ~2M and it's not worth making this repo harder to clone or download.

[PaulWAyers]

I'd encourage supporting binder. Beyond binder, it's pretty tricky....but I think binder is good enough.

[FarnazH]

@fwmeng88, I would remove the title of the sub-images and make a smaller version of them too (no need for high resolution), as you suggested.

[FanwangM]

@fwmeng88, I would remove the title of the sub-images and make a smaller version of them too (no need for high resolution), as you suggested.

The image has been updated accordingly, 20e8e42.