Improve error reporting

[AdamVig]

Instead of returning only a friendly error message as text/plain, return a JSON object containing the following fields:

{
  description: "Actual description of error message for debugging purposes"
  message: "User-facing message, ex: Something went wrong! 🆘 "
}

This change should also come with more descriptive use of error codes.

[AdamVig]

Restify comes with all of the HTTP status codes as error messages. See Restify Error Handling for more details. This could be a good way to throw errors in the app.

[AdamVig]

Restify error handling is excellent. Main improvements:

• Allows for removal of custom JSON formatter, which included some error handling.
• Relies on verbose function names describing the error codes (restify.UnauthorizedError()) instead of HTTP error codes (401), which makes for more readable code.
• Following the last point, the status code of the response is automatically set in regard to the error handler called, and the verbose description of the error code is sent in the response body.

The format of the error response is now JSON, like the following:

{
    "code": "BadGatewayError", 
    "explanation": "Something went wrong! 🆘", 
    "message": "Could not find chapel credits in HTML."
}