Implement notfound.org default 404 page

notfound.org is a great initiative. By default, Fork CMS wil now be
installed with a custom 404-page that will portay missing people,
increasing odds that someone, somewhere, may recognise someone...
Merge pull request #341 from matthiasmullie/master

Implement notfound.org default 404 page
Upgraded to CKFinder 2.3.1
Upgraded to CKEditor 3.6.6
Merge branch 'master' into release-3.5