Publish through JS

I doubt that this will be merged anytime soon into master, but this code allows clients to publish messages directly. Before you always had to call some rails code in order to publish messages in non-meta channels.

However, the contents published this way are not sanitized in any way or form. This should either be done by the receiving client or the faye server itself.

To control which channels a client may publish to you can add specify the option ``publish`` (default: false) when calling ``subscribe_to``:

````erb
<%= subscribe_to @channel.faye, publish: true %>
````