Autogenerate the admin section icon layout from a given image

Steps to reproduce:
Add a new Admin UI section to configure and application using using the http://extensions.xwiki.org/xwiki/bin/view/Extension/Administration+Application#HMakingyourapplicationconfigurablewithConfigurableClass.
Ex: Ratings

• install Ratings Application with Extension Manager
• configuration class: XWiki.RatingsConfigClass
• configuration document: XWiki.RatingsConfig
• attach the image attached in this issue(rating.png) to XWiki.RatingsConfig
• in the XWiki.ConfigurableClass added to the XWiki.RatingsConfig, add 'rating.png' to the iconAttachment field.

Expected result: When a new image is attached to the configuration document and refered in the iconAttachment field, the image layout should be autogenerated to look like the other entries images.