Allow widgets to choose not to propagate actions

Allow widgets to choose not to propagate actions. This is important for
widgets that themselves trigger actions.

Note that this change will cause problems with any existing
5.1.8-prerelease plugins that call `invokeActions()`.

core/modules/widgets/button.js

@@ -63,7 +63,7 @@ ButtonWidget.prototype.render = function(parent,nextSibling) {
 	// Add a click event handler
 	domNode.addEventListener("click",function (event) {
 		var handled = false;
-		if(self.invokeActions(event)) {
+		if(self.invokeActions(this,event)) {
 			handled = true;
 		}
 		if(self.to) {
@@ -94,6 +94,13 @@ ButtonWidget.prototype.render = function(parent,nextSibling) {
 	this.domNodes.push(domNode);
 };
 
+/*
+We don't allow actions to propagate because we trigger actions ourselves
+*/
+ButtonWidget.prototype.allowActionPropagation = function() {
+	return false;
+};
+
 ButtonWidget.prototype.getBoundingClientRect = function() {
 	return this.domNodes[0].getBoundingClientRect();
 }