trello: implement the ability to reopen

Only two states: `closed: true` and `closed: false`. Issues can also be deleted entirely. Then nothing happens.

![screenshot 2014-09-17 19 01 29](https://cloud.githubusercontent.com/assets/1079123/4314106/be91c0c0-3ed7-11e4-98b7-f3853957dfe3.png)