Add container widget

IPython/html/widgets/container/model.js

@@ -0,0 +1,2 @@
+var ContainerModel = IPython.WidgetModel.extend({});
+IPython.notebook.widget_manager.register_widget_model('container_widget', ContainerModel);

IPython/html/widgets/container/widget.py

@@ -0,0 +1,11 @@
+import os
+
+from ..widget import Widget
+from IPython.utils.traitlets import Unicode
+from IPython.utils.javascript import display_all_js
+
+class ContainerWidget(Widget):
+    target_name = Unicode('container_widget')
+    default_view_name = Unicode('ContainerView')
+    
+    _keys = []