Admin index models ordering

Hi,  I using admin page in my daily work.

But, Django admin/app index page **not** ordering the models what I want.

So, I add an additional argument `order_sequence` in the `register` method

```python
admin.site.register(ModelOne, ModelOneAdmin, order_sequence=2)
admin.site.register(ModelTwo, ModelTwoAdmin, order_sequence=1)
```

#### This will be useful when edit multi-related-models, Put this models together, It's More convenient for edit

Details see the diff.

And also the docs.

![docs](http://i1297.photobucket.com/albums/ag23/yueyoum/django-docs_zpsc8950ce8.png)


## Below shows the difference in my project

### The Default Admin

![default-admin](http://i1297.photobucket.com/albums/ag23/yueyoum/django-admin1_zpsd1146cc0.png)


### The Custom order Admin

![custom](http://i1297.photobucket.com/albums/ag23/yueyoum/django-admin2_zpsa8d0751f.png)