Disable parts of the timeline as the dates for them pass

As each date in the timeline passes, it will show as "disabled" to show that that item has passed. I've styled it as such:

![](https://cloud.githubusercontent.com/assets/494732/3321681/d692bfa6-f73a-11e3-8385-6b9bf4a47e23.png)

I don't think it is a tiny amount of logic: the helper would wrap both the `dt` and the `dd`, so it also wraps all the formatting. (This is logic of a kind too.) I'd like to see it attempted at least.