Noam Raphel: Further developemt of CodeContext feature.

The visibility state of the code context pane is now persistent between
sessions and the pane does not appear in the shell window.

M CodeContext.py
M EditorWindow.py
M NEWS.txt
M PyShell.py
M config-extensions.def
M configHandler.py

Lib/idlelib/PyShell.py

@@ -806,6 +806,9 @@ class PyShell(OutputWindow):
         #
         self.pollinterval = 50  # millisec
 
+    def get_standard_extension_names(self):
+        return idleConf.GetExtensions(shell_only=True)
+
     reading = False
     executing = False
     canceled = False