adding hbox and vbox

Conflicts:
	IPython/html/static/widgets/js/widget_container.js
	IPython/html/widgets/widget_container.py

IPython/html/static/widgets/js/widget_container.js

@@ -50,12 +50,23 b' define(['
     var FlexContainerView = ContainerView.extend({
         render: function(){
             FlexContainerView.__super__.render.apply(this);
+            this.model.on('change:orientation', this.update_orientation, this);
             this.model.on('change:flex', this._flex_changed, this);
             this.model.on('change:pack', this._pack_changed, this);
             this.model.on('change:align', this._align_changed, this);
             this._flex_changed();
             this._pack_changed();
             this._align_changed();
+            that.update_orientation();
+        },
+
+        update_orientation: function(){
+            var orientation = this.model.get("orientation");
+            if (orientation == "vertical") {
+                this.$el.removeClass("hbox").addClass("vbox");
+            } else {
+                this.$el.removeClass("vbox").addClass("hbox");
+            }
         },
 
         _flex_changed: function(){

IPython/html/widgets/__init__.py

@@ -14,7 +14,7 b' from .interaction import interact, interactive, fixed'
 # Deprecated classes
 from .widget_bool import CheckboxWidget, ToggleButtonWidget
 from .widget_button import ButtonWidget
-from .widget_container import ContainerWidget, PopupWidget
+from .widget_container import ContainerWidget, HBox, VBox, PopupWidget
 from .widget_float import FloatTextWidget, BoundedFloatTextWidget, FloatSliderWidget, FloatProgressWidget
 from .widget_image import ImageWidget
 from .widget_int import IntTextWidget, BoundedIntTextWidget, IntSliderWidget, IntProgressWidget

IPython/html/widgets/widget_container.py

@@ -37,6 +37,7 b' class Popup(Container):'
 
 class FlexContainer(Container):
     _view_name = Unicode('FlexContainerView', sync=True)
+    orientation = Unicode('vertical', sync=True)
     flex = Int(0, sync=True, help="""Specify the flexible-ness of the model.""")
     def _flex_changed(self, name, old, new):
         new = min(max(0, new), 2)