AUI-1044 - In aui-tree-node Add option to prevent selecting all child nodes in radio and task.

Hey @ipeychev,

Attached is an update for http://issues.liferay.com/browse/AUI-1044.  This is the backport version of https://github.com/ipeychev/alloy-ui/pull/26.

Please let me know if you have any questions.  Thanks!