Add role="presentation" into textbox of FocusPanel.
Without this role, VoiceOver miscounts a number of a list items if a
FocusPanel has the list, because the text box in the FocusPanel is also
counted.

Fixes issue 7597

Review at http://gwt-code-reviews.appspot.com/1803804

Review by: skybrian@google.com

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@11218 8db76d5a-ed1c-0410-87a9-c151d255dfc7