Removed jQuery code, small background fix

Firstly: no jQuery is needed to perform the simple task of setting links to `target="_blank"`. I rewrote this in pure JavaScript using the IE8+ DOM API. While this may result in slightly more ugly code, the benefit is a speedup of page load; not having to load jQuery and not having to use it.

Secondly, there was a major bug in the way that `background-size: cover` worked on Chrome for Android. It would display the webpage like this:

![image](https://cloud.githubusercontent.com/assets/6015058/5584806/cc7342d8-90ec-11e4-95a2-2a2e02b7d89b.png)

A simple fix to this is setting `height: 100%` on the element the background was set.