Added 404 page, subreddit redirect

This is a barebones 404 page replacing GH’s own. It doubles as a helping redirect for accessing subreddits with urls like redditate.com/r/aww

I am not able to test the page, but the code is pretty straightforward (I copied index.html, stripped anything that I deemed unnecessary on a 404 page and added a single comment + 2 lines of JS)