Added the DecoratorPanel, which is a Widget that wraps another Widget in a 9-box that can be used to create rounded corners.

Issue: 883
Patch by: jlabanca, ecc
Review by: ecc



git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@1875 8db76d5a-ed1c-0410-87a9-c151d255dfc7