Resume bars when app backs to foreground

iOS resumes UINavigationBar when app go back to foreground from background. It cause white navigation bar striped title color.

![ios may 7 2014 12 16 43 pm](https://cloud.githubusercontent.com/assets/113420/2898164/11b9f00c-d596-11e3-86bb-af665c6f4dd9.png)

This patch is modified DemoApp to resume bars manually when app backs to foreground.