Reduce the size of the 404 page

Changes:

* simplify the overall design
* remove Google search functionality as it does not provide much value
  in most cases
* reduce the overall file size, while keeping the gzipped size over 512
  bytes to prevent IE from displaying its own error page:
  http://www.404-error-page.com/404-error-page-too-short-problem-microsoft-ie.shtml

Benefits include:

* small file size (1405 bytes / 576 bytes gzipped), which is particular-
  ly useful when users are on a data plan and / or the server is wrongly
  configured (e.g.: tries to redirect to a "mobile" version of the web
  page and ends up serving a 404 page) or developers forgot to provide
  certain files (e.g.: /favicon.ico -
  http://zoompf.com/blog/2012/04/instagram-and-optimizing-favicons)
* improved performance (less HTTP requests, less memory consumption,
  faster rendering, etc.)
* designed to work with all kinds of screen sizes and support IE 6+