IOTA DIDComm connection protocol

[PhilippGackstatter]

Description of change

Implements the IOTA DIDComm connection protocol.

Links to any relevant issues

closes #842

Type of change

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• [ ] Bug fix (a non-breaking change which fixes an issue)
• [x] Enhancement (a non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Documentation Fix

How the change has been tested

Describe the tests that you ran to verify your changes. Make sure to provide instructions for the maintainer as well as any relevant configurations.

Change checklist

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• [ ] I have followed the contribution guidelines for this project
• [ ] I have performed a self-review of my own code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] New and existing unit tests pass locally with my changes