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.

I have assigned this to you to review since when you created this extension, you extended 'A.TreeNodeTask' on Git SHA ID https://github.com/liferay/alloy-ui/commit/8853a6129c9ca54a02c80ae1054203b1ecb8553f.  I think you should have extended 'A.TreeNodeCheck'.

Can you check and see if I broke anything or might have overlooked something?

Please let me know if you have any questions.  Thanks!