Fix OOCSIEvent property and parameter order

Example Processing code:

```java
    import nl.tue.id.oocsi.*;
    import nl.tue.id.oocsi.client.*;
    import nl.tue.id.oocsi.client.protocol.*;

    void setup() {
      OOCSI recipient = new OOCSI(this, "myrecipient", "localhost");
      recipient.subscribe("mychannel");

      OOCSIClient sender = new OOCSIClient("mysender");
      sender.connect("localhost", 4444);

      new OOCSIMessage(sender, "mychannel").data("mykey", "myvalue").send();
    }

    void handleOOCSIEvent(OOCSIEvent event) {
      println(
        event.getSender(),     // returned timestamp, now returns sender
        event.getRecipient(),  // returned sender, now returns recipient
        event.getChannel(),    // returned sender, now returns channel
        event.getTimestamp()); // didn't exist, now returns timestamp
      );
    }
````

The second commit is less trivial than the first one, but still very useful, e.g. to work with multiple OOCSIs handling events in one sketch.