update crate dependencies - ed25519-dalek and ed25519

[dmitris]

Description

As seen in the PR list, a number of the dependabot PRs fail CI builds because the dependency upgrades require some code changes. Thus the crate code "diverges" or falls behind the development of the dependencies and it may become more difficult to "catch up" later, or pick up desired new features, react to updates due to possible security issues etc.

This issue is for update of ed25519-dalek from 2.0.0-pre.0 to 2.0.0-rc.2 and the related upgrade of ed25519 from 2.1 to 2.2.1.