Add nicer mechanisms for browsing examples. Android has next/previous navigation and a listbox populated by the registered example names. iOS doesn't seem to have a built-in listbox I could find that worked easily so just left as a label for now - ideally we should make this like Android though as it's much slicker. The example factories are now aware of the example names, so they can be tested without instantiating them. The example lists in the view is driven sanely from the model. Currently the KeyboardInputExample does not behave well when scrolling through the examples, leading to crash on exit -- this example has been disabled for now.