(NOTE: this includes all other folders that the message belongs to,
including 'INBOX' for example).

Create a route to get a list of messages in JSON, tied to a hard-coded
email account for now.

For easy JSON output

Dammit Context.IO Ruby SDK

I need a ContextIO instance in another module class so let's create a
base class so I don't have to keep doing it.

REQUEST_URI already has a trailing slash so we shouldn't be adding a
second one.