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

sky/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>