add angular-resource
add separate auth service
better encapsulation of authentication and xhr

- Add a response interceptor to the httpProvider so that the
  FlashProvider can unwrap the server responses, handle the flash
  messages, and pass along only the real result to the rest of the
  application.
- Accept JSON params to /app POSTs and clean up content negotiation.
- Use $resource to create an angular service for authentication.
- Encapsulate some global scope variables by using isolates and
  directives for the user picker and auth tabs.
Merge branch 'auth-and-flash-service-refactor' into develop