Implementing OAuth 2.0 enabled APIs

  - APIs: GET /api/sweets/q, POST /api/sweets, GET /api/users/me are now OAuth
    2.0 enabled. That means registered clients can use these APIs to sweet to
swtstore and retrieve swts from the swtstore.
  - Implement CORS headers in APIs and Persona login URLS, so that swtstore can
    support cross-domain, cross-origin requests.
  - README changes to better explain how to install and run this application.