原因分析：在StoryBoard中没有一个view controller设置了Initial Scene。
解决方案：在Storyboard中，选择一个view conroller作为story board的第一启动界面
Failed to instantiate the default view controller for UIMainStoryboardFile 'Main' - perhaps the designated entry point is not set?
原文：http://www.cnblogs.com/canf/p/4903997.html
