Add functionality for an application to have an API

Summary

Adds support for communication between Labrador applications.

Checklist

All items on this checklist should be checked.

• I have added a changelog entry.
• I have added tests for the functionality that I added.
• I adhere to the style guide.

Technical details

The authentication workflow is as follows:

• App 1 asks core where 'App 2' is located
• App 1 sends a request to /api/authenticate on App 2
• App 2 asks core to see if App 1 is an authenticated Labrador app
• App 2 generates an API token valid for 1 hour and sends it to App 1
• App 1 can then communicate with App 2 without help from core until the token expires