Added ability to get queue name from method

[chrishardinge]

When using Pusher, in order to specify which queue to use, public $broadcastQueue = 'name_of_queue' must be set.
Unfortunately, all public variables set in the event are sent onto Pusher - resulting in the end user receiving this, in addition to the intended payload.

Steps To Reproduce:

Create an event, specifying public $broadcastQueue, and run the worker.
Watch for the event in a web app, or simply use the "Debug Console" in Pusher to see the payload.

Usage

//  SendPushEvent.php
...
public function broadcastQueue()
{
    return 'name_of_queue';
}

I figure this would be consistent with broadcastOn and broadcastAs.

Does anyone have any thoughts on the matter?

[taylorotwell]

This fix is fine. But we should also remove it from the Pusher payload to fix that bug. @themsaid