Debug mode that will show a nice formatted page when an expcetion is raised

This PR adds a new `debug` parameter to the application that will be injected into `ExceptionHandler`. If in debug mode, exception handlers will not be called, but instead a nice formatted page will be shown:

![Debugging Page](https://cloud.githubusercontent.com/assets/145141/4673656/bf03745a-55a6-11e4-855c-1cdad53f6c5a.png)

Let me know what you think.