Add setting to control whether tree items are scrolled into view when selected.
Adapted from patch http://gwt-code-reviews.appspot.com/1819803/
Credit for the original patch goes to Marko Krajnc (marko.krajnc@cursor.si)

Fixes issue 2467.

Review by: mdempsky@google.com

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@11465 8db76d5a-ed1c-0410-87a9-c151d255dfc7