Add proper JSON API error response when a request is Unauthorized

[marsbergen]

Context

For example when accessing /private/demo without a valid access token the default Vert.x exception handler is used. Therefor we are missing the JSON API structured error we do return when other exceptions occur.

Currently failed requests result in the following logging:

SEVERE: Unhandled exception in router
io.vertx.ext.web.handler.HttpException: Unauthorized

Technical Requirements

• Add Vert.x failureHandler to the router which converts a standard Exception into a JSON API error response as we do for other endpoints.