Bug 1091007 - Don't add items to collapsed groups. r=kgrandon

I think we pretty much need to do this logic 100% of the time, except on the first configuration. TBH I'm not sure if this is being called on the first config, that code is kind of a mess. The problem is if we don't do this every time, then the home screen can be easily OOM killed when we are in the marketplace on lower-end devices.

You can see this by doing something like: 
```
adb shell
b2g-ps
kill -9 <home screen pid>
```