Rationalize Dart mojo and sky package structure

examples/dart/console_example/main.dart

 // 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 'dart:async';
 
-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/console.mojom.dart';
 
 class ConsoleApplication extends Application {
   ConsoleProxy _console;
 
   ConsoleApplication.fromHandle(MojoHandle handle) : super.fromHandle(handle);
 
   void initialize(List<String> args, String url) {
     _console = new ConsoleProxy.unbound();
     connectToService("mojo:console", _console);
     run();
   }
 
   run() async {
     var result = await _console.ptr.readLine();
     await _console.ptr.printLines([result.line]);
 
     _console.close();
     await close();
     assert(MojoHandle.reportLeakedHandles());
   }
 }
 
 main(List args) {
   var appHandle = new MojoHandle(args[0]);
   new ConsoleApplication.fromHandle(appHandle);
 }