Rename mash_shell to mash_session.

mash/session/public/interfaces/session.mojom

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-module mash.shell.mojom;
+module mash.session.mojom;
 
 interface ScreenlockStateListener {
   // This method is called when the listener is initially added with the current
   // lock state, and subsequently whenever the lock state changes.
   ScreenlockStateChanged(bool locked);
 };
 
-interface Shell {
+interface Session {
   Logout();
   SwitchUser();
   LockScreen();
   UnlockScreen();
   AddScreenlockStateListener(ScreenlockStateListener listener);
 };