Collapse/Expand all

```
Would be nice to have a way for the user to collapse all foldable node at once 
and subsequently expand all (and have both options available when some but not 
all nodes are collapsed).
```

Original issue reported on code.google.com by `W.Elwoo...@gmail.com` on 30 May 2011 at 1:29
- Blocking: #15
