Added style getters to UiRenderers

Now UiRendered templates with <ui:style>s can be retrieved with a getter.

Review at http://gwt-code-reviews.appspot.com/1700803

Review by: rdayal@google.com

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@11028 8db76d5a-ed1c-0410-87a9-c151d255dfc7