An public activity jsonp outbox at /api/user/<nickname>/feed/public without login

This enables a public jsonp stream. Jsonp works from other servers (json same-origin policy)

You can easy use it with JavaScript:

```

<html>
<head>

<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js">
</script>
<script>

$(document).ready(function(){
  $("button").click(function(){

     $.getJSON("https://io.intevation.de/api/user/Intevation/feed/public?callback=?", function(data){ callback(data); } )

   });
});

</script>

<script>
function callback (json) {

  $(".results").append("loaded...");

  alert(json.displayName);

}
</script>

</head>
<body>
<div class="results">Data:</div>
<button>Get Data</button>
<div></div>

</body>
</html>
```