provide access to celluloid's exception handler

Hi Brandon, this pull request adds access to celluloid's exception handler so that one can use his own - just the way one can use his own logger. To visualize this I added an exception handler to the example_app, that saves exceptions in an array called CRASHES (similar to the STORE array). The contents of this array is shown in the view and you can also "add a crashing job" with a button.