Refactor some hard to change test data.

The test data in [`opengever.task.tests.data`](https://github.com/4teamwork/opengever.core/blob/6737c4d728d5d8356d12ea42af6c82ed6c8ee62c/opengever/task/tests/data.py) is nearly impossible to update or even read.

This PR changes it to be pretty printed Python, that then dynamically gets converted to JSON, resulting in the same data but better readability. We might still need to revisit that test though ;)