Add option to not focus on widgets when created

Allow widget definitions to include a "focusOnCreate" flag which tells the
widget whether or not to grab focus immediately after being created. This flag
defaults to true, which is the same as the previous behavior.

Closes #6

plugins/widget/plugin.js

@@ -426,7 +426,7 @@
 		 *
 		 * * inserting widget element into editor,
 		 * * marking widget instance as ready (see {@link CKEDITOR.plugins.widget#event-ready}),
-		 * * focusing widget instance.
+		 * * focusing widget instance if focusOnCreate is set (default)
 		 *
 		 * This method is used by the default widget's command and is called
 		 * after widget's dialog (if set) is closed. It may also be used in a
@@ -465,7 +465,9 @@
 				// Fire postponed #ready event.
 				widget.ready = true;
 				widget.fire( 'ready' );
-				widget.focus();
+				if ( widget.focusOnCreate ) {
+					widget.focus();
+				}
 			}
 		},
 
@@ -978,6 +980,11 @@
 
 			draggable: widgetDef.draggable !== false,
 
+			/**
+			 * Whether a widget should automatically be focused when it is created.
+			 */
+			focusOnCreate: widgetDef.focusOnCreate !== false,
+
 			// WAAARNING: Overwrite widgetDef's priv object, because otherwise violent unicorn's gonna visit you.
 			_: {
 				downcastFn: ( widgetDef.downcast && typeof widgetDef.downcast == 'string' ) ?
@@ -4811,6 +4818,13 @@
  * @property {Boolean} draggable
  */
 
+/**
+ * Whether widget should be focused on creation. Defaults to `true`.
+ * If set to `false` the widget won't have focus immediately after creation.
+ *
+ * @property {Boolean} focusOnCreate
+ */
+
 /**
  * Names of element(s) (separated by spaces) for which the {@link CKEDITOR.filter} should allow classes
  * defined in the widget styles. For example, if your widget is upcasted from a simple `<div>`