Add capability for widgets to trigger all descendant action widgets, rather than just immediate children.

Preserves compatibility with existing invokeActions call in button widget by creating a separate 'invokeActionCall' function to carry out the recursion.  Triggering all descendants permits use of action widgets inside list widgets or macros.  Also makes it possible to add triggering capability to select widget.

core/modules/widgets/widget.js

@@ -476,15 +476,25 @@ Widget.prototype.removeChildDomNodes = function() {
 };
 
 /*
-Invoke any action widgets that are immediate children of this widget
+Invoke any action widgets that are descendants of this widget.
 */
 Widget.prototype.invokeActions = function(event) {
+	return this.invokeActionCall(this, event);
+};
+
+/*
+Recursively search through descendants, invoking all actions encountered.
+*/
+Widget.prototype.invokeActionCall = function(here, event) {
 	var handled = false;
-	for(var t=0; t<this.children.length; t++) {
-		var child = this.children[t];
+	for(var t=0; t<here.children.length; t++) {
+		var child = here.children[t];
 		if(child.invokeAction && child.invokeAction(this,event)) {
 			handled = true;
 		}
+		if(this.invokeActionCall(child, event)) {
+			handled = true;
+		}
 	}
 	return handled;
 };