PRIPAD-5194 Tidy up HTML out of PHP

In the current version of HockeyKit it has the various pages that render displaying an app all jammed in the same index.php inbetween a load of `if`'s. 

I've modified this to use a `view` class, and a `renderer` class to render the page that's been requested, and all the HTML now lives in a `views` directory. The views contain placeholders that are replaced at runtime from within the `renderer` which should help with maintainability.