Use IDs rather than names everywhere programmatic identifiers are needed

[SeanKilleen]

Names and orgs can change on GitHub. Need to be conscious of using IDs where we can.

• PersistentRepoActor uses the name in the Persistence ID
• PersistenUserActor uses the org name in the AddOrgForUserCommand, but would need to discover the org ID before processing the command in that case.