Add devlogin to simulate production EasyAuth

[c-w]

In production we don't need to pass any authorization headers since the Easy Auth redirect sets up the appropriate cookies for us. During local development, we can emulate the same authentication by grabbing an ID Token from Active Directory and passing it as the Authorization header. This pull request implements a flow to make it super easy to grab the ID token: simply head to http://localhost:3000/devlogin, click the link which will redirect to B2C. Once the login is complete, B2C will redirect back to localhost which will in turn stash the ID Token in local storage so that requests can then access it. Any API request should use the new util/request method which automatically passes through the Authorization header if the developer went through this login flow.