Add back simplytest.me button

Initial attempt at solving https://github.com/dreditor/dreditor/issues/46, looks fine visually (or at least similar to the D6 one) and works as expected but I'm not sure I like the markup order (simplytest.me button first, then review button).

The selector for finding the issue version is… less ideal but should work the same.

Screenshot:
![dreditor-d7-simplytest](https://f.cloud.github.com/assets/327943/1458364/8d2bd9f8-4365-11e3-8fa6-43400a7c77fb.png)