Improve contrast of editable fields within "parts"

* Publisher users use the white on grey contrast to identify fields they need to edit, the white background of the default panel hides the form fields from users scanning the page
* Give the panel a darker background, and make the title of the panel darker still
* Improve vertical alignment of Parts headers

![screen shot 2014-06-24 at 16 20 16](https://cloud.githubusercontent.com/assets/319055/3373384/1744b974-fbb3-11e3-9fb1-9f836497a53a.png)