bpo-35769: Change IDLE's name for new files from 'Untitled' to 'untitled' (GH-11602)

'Untitled' violates the PEP 8 standard for .py files
diff --git a/Lib/idlelib/NEWS.txt b/Lib/idlelib/NEWS.txt
index a458c39..222f187 100644
--- a/Lib/idlelib/NEWS.txt
+++ b/Lib/idlelib/NEWS.txt
@@ -3,6 +3,8 @@
 ======================================
 
 
+bpo-35769: Change new file name from 'Untitled' to 'untitled'.
+
 bpo-35660: Fix imports in window module.
 
 bpo-35641: Properly format calltip for function without docstring.
diff --git a/Lib/idlelib/editor.py b/Lib/idlelib/editor.py
index d13ac37..e05b52a 100644
--- a/Lib/idlelib/editor.py
+++ b/Lib/idlelib/editor.py
@@ -943,7 +943,7 @@
         elif long:
             title = long
         else:
-            title = "Untitled"
+            title = "untitled"
         icon = short or long or title
         if not self.get_saved():
             title = "*%s*" % title
@@ -965,7 +965,7 @@
         if filename:
             filename = os.path.basename(filename)
         else:
-            filename = "Untitled"
+            filename = "untitled"
         # return unicode string to display non-ASCII chars correctly
         return self._filename_to_unicode(filename)