Simplified construction of complex messages

- can now provide all data, incl. for sub-messages, directly in
  message constructor. E.g.:

```js
  let now = Date.now();
  let secs = parseInt(now/1000);
  let nsecs = (now % 1000) * 1000;
  let shapeMsg = new shapeActionGoal({
    header: {
      seq: 0,
      stamp: {
        secs: secs,
        nsecs: nsecs
      },
      frame_id: ''
    },
    goal_id: {
      stamp: {
        secs: secs,
        nsecs: nsecs
      },
      id: "/my_node-1-"+secs+"."+nsecs+"000"
    },
    goal: {
      edges: 5,
      radius: 1
    }
  });
```

Author: chfritz

utils/messages.js

@@ -505,7 +505,16 @@ function buildMessageClass(details) {
 
     if (values) {
       Object.keys(values).forEach(function(name) {
-        that[name] = values[name];
+        var type = details.fields.find(function(field) {
+          return field.name == name;
+        });
+        console.log("Message", name, type);
+        if (type.messageType) {
+          console.log("Message", name, type.messageType);
+          that[name] = new (type.messageType)(values[name]);
+        } else {
+          that[name] = values[name];
+        }
       });
     }
   };