Fix sorting of accrodion widget to match the set order.

#5268 

I managed to reproduce the bug mentioned in https://github.com/openscholar/openscholar/issues/5268#issuecomment-41568272

After changing the selector in the JS file I see the order matches in both the settings and the rendered widget:
![selection_116](https://cloud.githubusercontent.com/assets/4497748/2825994/39719abc-cf62-11e3-94b0-85247eb72168.png)
![selection_117](https://cloud.githubusercontent.com/assets/4497748/2825991/24b26f52-cf62-11e3-944e-9a3e5ed33886.png)

The original selector ``$('.field-weight', $form)`` was with length 0 as the elements in the form are rendered with the class ``widget-weight`` instead.