sprintly: implement reopening of issues

Only `backlog`, `in-progress`, `completed`, and `accepted` are valid values for issues. We mark them as `in-progress`, when they reoccur.

![screenshot 2014-09-17 17 05 26](https://cloud.githubusercontent.com/assets/1079123/4313338/9640f5e2-3ec7-11e4-958d-c75af0b4751b.png)