Augment home focus handler for IE 11/video splash. Bug 1101964.

Debugging through IE 11 dev tools, it appears the `<body>` on the home page on production is getting focus on page load, which is odd, because I don't think `<body>` is supposed to get focus?

![body-focus](https://cloud.githubusercontent.com/assets/317532/5117632/e5fa31bc-701c-11e4-8719-df523f0a922b.png)

I can't reproduce the error from my local instance.

I tried on demo3 (which had a couple day old rebased branch) and was able to reproduce. I added a bit of debugging code and pushed to demo3 to test again. After that push, I could no longer reproduce the error.

This branch is currently on [demo2](https://www-demo2.allizom.org/), but I still can't reproduce the error. The code here works, but since I can't reproduce the error, I'm not 100% certain it's an actual fix. (It does improve things a little by removing the focus handler though.)

I'm wondering if there is some issue with the minified JS file on the CDN?
Yeah, I wasn't sure of the best route here. As far as I read, there's not really a standard as to which elements can receive focus. It doesn't really work to try to delegate focus from `<body>` or any other container. I ended up with `*` to accommodate whatever the browser thinks should be focusable.

I suppose we could go back to the original list (`a, input, textarea, button`) if those are the only elements we think should cause the splash to disappear.