Implement collapsible Fieldset widget, based on initial code from Jens Arps (CLA on file), thanks!   Fixes #10171.  Not sure if this should go in dijit or dijit/form though.  Put it in dijit/ for now.
Implement collapsible Fieldset widget, based on initial code from Jens Arps (CLA on file), thanks!   Fixes #10171.  Not sure if this should go in dijit or dijit/form though.  Put it in dijit/ for now.

git-svn-id: 674a2d6b1e32e53f607eb824547723f32280967e@30990 560b804f-0ae3-0310-86f3-f6aa0a117693

kitsonk/delite,harbalk/delite,harbalk/delite,Sam-Cummins/delite,Sam-Cummins/delite,kitsonk/delite