allowing the ability to show joke on screen

had to call the function on the main thread in order to
reflect the changes in the UI.
added the refresh button to refresh a joke.
adding the picture.  At this time, it is not random.
adding urls for chuck norris images
Dan McCracken helped to clean the ui...whew...cause it was ugly
applying the same style to the second controller
created a JokeController to control the flow of the datamodel.
using simple singleton pattern create only one instance of JokeController
Merge pull request #33 from chenry/feature/show_joke_on_ui

allowing the ability to show joke on screen