Pryvote shamir protocol

[TTitcombe]

Description

This PR:

• adds a notebook demoing the Shamir Secret Sharing voting protocol
• minor aesthetic changes to the SMPC voting notebook

Affected Dependencies

None

How has this been tested?

• Notebooks run

Checklist

• [X] I have followed the Contribution Guidelines and Code of Conduct
• [X] I have commented my code following the OpenMined Styleguide
• [X] I have labeled this PR with the relevant Type labels
• [X] My changes are covered by tests

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[Horus888]

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[wip-abramson]

Apologies for the delay Tom. This is really cool. You can see how it would be extended with SSI for the send vote part too