Improve keyboard support of websites

These patches improve the support for keyboard navigation: when loading the URL shortener web page, the input field is automatically focussed so that you can start typing (or, more likely, pasting) an URL to shorten right away. On the page showing the shortened URL, the shortened URL is automatically selected so that you can press Ctrl+C right away to copy it instead of having to use the mouse to select it.

There's one patch which just adds a DOCTYPE declaration to the generated HTML; it's not related to the keyboard support, but I thought it's a nice little improvement anyway (and I was just too lazy to strip the commit). ;-)