Rationalize Dart mojo and sky package structure

examples/dart/netcat/main.dart

 // Copyright 2014 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 'dart:async';
 import 'dart:core';
 import 'dart:typed_data';
 
-import 'package:mojo/public/dart/application.dart';
-import 'package:mojo/public/dart/bindings.dart';
-import 'package:mojo/public/dart/core.dart';
+import 'package:mojo/application.dart';
+import 'package:mojo/bindings.dart';
+import 'package:mojo/core.dart';
 import 'package:mojom/mojo/files/file.mojom.dart' as files;
 import 'package:mojom/mojo/files/types.mojom.dart' as files;
 import 'package:mojom/mojo/net_address.mojom.dart';
 import 'package:mojom/mojo/network_error.mojom.dart';
 import 'package:mojom/mojo/network_service.mojom.dart';
 import 'package:mojom/mojo/tcp_bound_socket.mojom.dart';
 import 'package:mojom/mojo/tcp_connected_socket.mojom.dart';
 import 'package:mojom/mojo/terminal/terminal_client.mojom.dart';
 
 void ignoreFuture(Future f) {
@@ skipping 180 matching lines @@
 }
 
 main(List args) {
   MojoHandle appHandle = new MojoHandle(args[0]);
   String url = args[1];
   new NetcatApplication.fromHandle(appHandle)
     ..onError = (() {
       assert(MojoHandle.reportLeakedHandles());
     });
 }