Update 404 Page. 

The 404 page for invalid application paths was using the old website design, and missing CSS and JS references. Updated the page to the new 404 styling, and updated the redirect links. 

@davideaster, @scottnc27603 Can one of you please review?
While we're here ... the license isn't known as *Apache II*. We should refer to it as either "Apache 2", or use the terminology in the license: "Apache License, Version 2.0". It looks like `/index.html` is the only other reference.