PlannedFor lookup is limited to the first 1000 iterations

Hi @dixudx,

I'm seeing the following behaviour in Jazz 6.0.3.

With an example server containing 2738 iterations the lookup of the iterations in `_getPlannedFors` will only return the first 1000 iterations and thus resulting in an error if creating an WorkItem of a newer iteration.

This happens because the first request results in:
```

```
But following the next link the totalCount has changed and thus limiting the logic in `client.py:1410` to the first 1000 iterations.
```

```
I'm experimenting on how to avoid this limit.