Patch for /trunk/gviz_api.py

```
Allows a DataTable to have a default columns_order and order_by, which are used 
if none is specified in one of the export calls.
```

Original issue reported on code.google.com by `isam...@google.com` on 13 Nov 2014 at 8:40

Attachments:
- [gviz_api.py.patch](https://storage.googleapis.com/google-code-attachments/google-visualization-python/issue-26/comment-0/gviz_api.py.patch)
