Add 'Awaiting review' column

https://www.agileplannerapp.com/boards/173808/cards/8711

![screenshot - 031214 - 12 29 00](https://cloud.githubusercontent.com/assets/93511/5280359/ff63676a-7ae7-11e4-9df7-065980cd9caa.png)

From the state_machine docs https://github.com/pluginaweek/state_machine
_The bang (!) operator can raise exceptions if the event fails_