Tools for migrating to a new ID

[NfNitLoop]

If a userID is compromised, or its private key is lost, there should be some tool(s) for migrating content to a new userID (pub/priv key pair).

• [ ] The tool should scan all content for a key, and re-post it under a new userID.

Optional features:

• [ ] Preview items of content before reposting them.
• [ ] Server-side integration to allow doing this for userIDs that have been revoked? #5