Issue #24225: Within idlelib files, update idlelib module names.

This follows the previous patch that changed idlelib file names.
Class names that matched old module names are not changed.
Change idlelib imports in turtledemo.__main__.

Exception: config-extensions.def.  Previously, extension section
names, file names, and class names had to match.  Changing section
names would create cross-version conflicts in config-extensions.cfg
(user customizations).  Instead map old names to new file names
at point of import in editor.EditorWindow.load_extension.

Patch extensively tested with test_idle, idle_test.htest.py, a custom
import-all test, running IDLE in a console to catch messages,
and testing each menu item.  Based on a patch by Al Sweigart.

Lib/idlelib/iomenu.py

@@ -10,7 +10,7 @@ import tkinter.filedialog as tkFileDialog
 import tkinter.messagebox as tkMessageBox
 from tkinter.simpledialog import askstring
 
-from idlelib.configHandler import idleConf
+from idlelib.config import idleConf
 
 
 # Try setting the locale, so that we can find out
@@ -107,6 +107,9 @@ def coding_spec(data):
 
 
 class IOBinding:
+# One instance per editor Window so methods know which to save, close.
+# Open returns focus to self.editwin if aborted.
+# EditorWindow.open_module, others, belong here.
 
     def __init__(self, editwin):
         self.editwin = editwin