Register new widgets in IPython.html.widgets namespace

IPython/html/widgets/__init__.py

@@ -1,1 +1,7 b''
-from widget import Widget
  No newline at end of file
+from widget import Widget
+
+from container import ContainerWidget
+from float_range import FloatRangeWidget
+from int_range import IntRangeWidget
+from selection import SelectionWidget
+from string import StringWidget