hc-dpki cli for DeepKey

[zo-el]

PR summary

Adds some new commands to the CLI tool for managing DPKI keys.

• hc dpki genroot creates a new random root seed
• hc dpki keygen is similar to hc keygen but will use a dpki root seed mnemonic so that keys can be recovered
• hc dpki genrevoke/genauth produce revocation/auth seeds from which keys can be derived.
• hc dpki sign use a revocation/auth seed to produce a key then sign a message (which can be an agent key). This is the process by which keys can be authorized and revoked

Each time a mnemonic is produced it is optionally encrypted with a passphrase

testing/benchmarking notes

( if any manual testing or benchmarking was/should be done, add notes and/or screenshots here )

followups

( any new tickets/concerns that were discovered or created during this work but aren't in scope for review here )

changelog

• [ ] if this is a code change that effects some consumer (e.g. zome developers) of holochain core, then it has been added to our between-release changelog with the format

- summary of change [PR#1234](https://github.com/holochain/holochain-rust/pull/1234)

documentation

• [ ] this code has been documented according to our docs checklist

[zippy]

@zo-el I notice a bunch of tests are breaking, would like to review this after tests pass...

[zo-el]

@zo-el I notice a bunch of tests are breaking, would like to review this after tests pass...

Yes @zippy, this is still work in progress. I apologise.

[zo-el]

@zippy this PR is ready for review