bpo-37892: Use space indents in IDLE Shell (GH-25678)

Adding a newline to the prompt moves it out of the way of
user code input, which now starts at the left margin,
along with continuation lines.
diff --git a/Lib/idlelib/pyshell.py b/Lib/idlelib/pyshell.py
index 5830b7a..447e9ec 100755
--- a/Lib/idlelib/pyshell.py
+++ b/Lib/idlelib/pyshell.py
@@ -889,11 +889,11 @@ def __init__(self, flist=None):
 
         OutputWindow.__init__(self, flist, None, None)
 
-        self.usetabs = True
+        self.usetabs = False
         # indentwidth must be 8 when using tabs.  See note in EditorWindow:
-        self.indentwidth = 8
+        self.indentwidth = 4
 
-        self.sys_ps1 = sys.ps1 if hasattr(sys, 'ps1') else '>>> '
+        self.sys_ps1 = sys.ps1 if hasattr(sys, 'ps1') else '>>>\n'
         self.prompt_last_line = self.sys_ps1.split('\n')[-1]
         self.prompt = self.sys_ps1  # Changes when debug active