Move terminal example from //sky/examples to //examples

examples/terminal/index.sky

 #!mojo mojo:sky_viewer
 <!--
 // Copyright 2015 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.
 -->
 <import src="terminal.sky" />
 <!--
 <terminal id="terminal" url="mojo:echo_terminal" />
 -->
 <terminal id="terminal" />
 <script>
 import 'dart:core';
 import 'dart:sky';
 
 main () {
   var terminal = document.getElementById('terminal');
   var params = Uri.parse(document.URL).queryParameters;
   if (params.containsKey('url')) {
     terminal.connect(params['url']);
   } else {
     terminal.putString('HALP: Add a "?url=<URL>" query.\n'
                        'E.g., "?url=mojo:echo_terminal".\n');
   }
 }
 </script>