Implement #66: Some kind of logo/image

Implements and closes #66.

The logo is based on @MaPePeR's logo, latest version (Eye of Providence, clock instead of eye, brick background, clock in upper half); I animated the clock and added the text "at your own pace" in the low half.

I'm very happy with the logo (the clock-setting script is even in the SVG; it's self-contained!), but not really with its position inside the document: I just stuffed it in the header. Surely there's a better location for it?

Also, this doesn't yet implement the "control which image facebook uses to represent your site" thingy @MaPePeR outlined in [this comment](https://github.com/deplicator/xkcdTime_atyourownpace/issues/66#issuecomment-18672282).

The logo was tested and works in Firefox 24.0a2 and Chromium 28.0.1500.71.