Add crate logos-accounts

[jazzz]

Accounts were introduced in a previous PR however they were local to the core/conversations. This PR moves Accounts to their own crate so they can be re-used in other services.

Changes:

• Adds IdentityProvider trait to service_traits so it is available for external implementors.
• Adds logos-account crate, as it need to be accessible by applications to administer user accounts. This change while perhaps permature, establishes it as an external entity.
• Updated IdentityProvider::friendly_name -> display_name as suggested by @osmaczko .

Future Work:

• Update core::context to accept an external IdentityProvider impl on construction.
• Update InboxV2 to use this

[jazzz]

This PR is dependent on #101 being merged first.