Fix # web users graph

fixes http://manage.dimagi.com/default.asp?144599#805971

reimplements a broken query
I'm not sure how I feel about this formatting.. Anyone else have thoughts? Not saying you need to change this, just was hoping to spark a conversation maybe?

I think I normally do this:
```
    query.created(
        lt=datespan.startdate
    ).run(
        blah=blah
    ).doc_ids
```

But also don't mind:

```
query.created(..)
     .date_histogram(...)
     .run()
```