Move the implementations of methods in Role to RoleImpl, to reduce duplication
in the RoleImpl subclasses. Reduces the lines of source code in aria/client by 65%.

Review at http://gwt-code-reviews.appspot.com/1808804

Review by: atincheva@google.com

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@11220 8db76d5a-ed1c-0410-87a9-c151d255dfc7