disk space: make it easy to manager

Basically, do this:
```
~$ du -sh * .[!.]* | grep -v .snapshots | sort -h
```

But for a UI, maybe 

```
~$ du -sh * .[!.]* 
```
streaming the output to the frontend, then sorting as new output appears, with links to each directory, and maybe some heuristic knowledge about what is safe to delete...