Mojo: Move mojo/public/shell to mojo/public/{cpp,interfaces}/shell.

mojo/public/interfaces/shell/shell.mojom

 // Copyright 2013 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 mojo {
 
 [Peer=ShellClient]
 interface Shell {
   // Loads url. mojo:{service} will result in the user of the value of the
   // --origin flag to the shell being used.
   Connect(string url, handle<message_pipe> client_handle);
 };
 
 [Peer=Shell]
 interface ShellClient {
   AcceptConnection(string url, handle<message_pipe> client_handle);
 };
 
 }