Feature request: add logout command to clear login data from disk

[iTrooz]

See the title :)

[acheong08]

This should be pretty easy since we just have to delete .config/hydroxide/<username>.db and update auth.json. Not sure what the expected behavior should be for currently running servers though since the database would still be open somewhere. We'd need to be able to send signals to the running hydroxide service and tell it to end any imap connections to that user and close the database. Should hydroxide have an internal api to allow the cli to manage other instances?