Add string widget

IPython/html/widgets/string/model.js

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

IPython/html/widgets/string/widget.py

@@ -0,0 +1,14 @@
+import os
+
+from ..widget import Widget
+from IPython.utils.traitlets import Unicode, Bool
+from IPython.utils.javascript import display_all_js
+
+class StringWidget(Widget):
+    target_name = Unicode('StringWidgetModel')
+    default_view_name = Unicode('TextboxView')
+    _keys = ['value', 'row_count', 'disabled']
+    
+    value = Unicode()
+    disabled = Bool(False) # Enable or disable user changes
+