Support for Server-Sent-Events

If the Backend provides an API with Content-Type "application/stream+json" or "text/event-stream" swagger-ui should use an EventSource instead of sending ajax http-requests.

code:
var evtSource = new EventSource('http:server.domain.com/context_path)');
evtSource.onerror = function(e) {
console.log(e.data);
}
evtSource.onmessage = function(event) {
console.log(event.data);
}

instead of logging the data it should be displayed in the response field.

For IE-Support maybe it is necessary to include an polyfill.
e.g.: eventsource.js from https://github.com/Yaffle/EventSource/

Start by locating Swagger UI's request handling and response display code, then inspect how application/stream+json and text/event-stream responses are currently processed. Compare the EventSource behavior described in the issue, including the optional eventsource.js polyfill, and verify that streamed data appears in the response field instead of being handled as a regular AJAX request.