Add Account-log + Account

[jazzz]

Problem

Accounts and multi device keys are currently handled in a subpar way which makes handling and revocation difficult.

Solution

This PR adds an eventual replacement for handling Account management in the logos ecosystem.

Its implementation is based on the AccountLog Specification (logos-co/logos-lips#404)

AccountLogs are an wire encoding for collection of updates. Users can Add, and Remove entries to endorse keys and associate data.

Accounts are currently based on an owned SigningKey for authentication.

Notes

• Accounts are not integrated into the ChatClient in this PR. They are solely submitted for review as is along with the companion specification.
• Storage, and distribution are not covered here, and will be followup PRs.
• Exposes traits for AccountProvider(read) and AccountPublisher(write) to define an interface between implementors and consumers