Add chat topic

It's hard to see the description of the mapping task often, so to make it more relevant, I added it to the chat UI as a 'topic'.

![screenshot from 2013-08-18 17 13 47](https://f.cloud.github.com/assets/365751/982226/2c399ec6-07da-11e3-8a53-4f64ed23a282.png)