Reference composite usage needs to be reimplemented

Currently #setAsReference() needs to be called whenever you need to jump out to upper composite. This can lead to errors when user forget to set reference composite. This should be reimplemented to be used in constructors like this:

```java
Group g = new DefaultGroup("Group label");
new LabeledText(g,"Name:").setText("value");
```

rather than current approach below
```java
Shell s = new DefaultShell("Preferences");
new DefaultGroup("Group label");
new LabeledText("Name:").setText("value");
s.setAsReference();
```