Fancy error page for topic lists

> ![image](https://cloud.githubusercontent.com/assets/627891/3321712/4e27befe-f73b-11e3-9224-0b432e6e644f.png)

> ![image](https://cloud.githubusercontent.com/assets/627891/3344026/5954cec2-f8a6-11e3-9af2-8b4d884001c3.png)


This page will come up if the `model` function in the route's promise is rejected.

#### Known Issues
If you go from a category filter (e.g. Meta:Latest) to another category filter (e.g. Meta:New), get an error, and successfully retry, an extra `undefined/` will be inserted in your URL. This does not persist after navigating anywhere else.