Merge pull request #253 from Unity-Technologies/fix_editorwindow_mousemove_event

enable wantsMouseMove events on editorWindow

com.unity.uiwidgets/Editor/UIWidgetsEditorPanel.cs

 
         void OnEnable() {
             D.assert(_wrapper == null);
+
+            //enable listener to MouseMoveEvents by default
+            //user can disable it in onEnable() if needed
+            wantsMouseMove = true;
+            
             _configurations = new Configurations();
             _wrapper = new UIWidgetsPanelWrapper();
             onEnable();