Implement Simpletest

Hi Greg,

I read the article on unit testing (http://www.lullabot.com/articles/introduction-unit-testing) and I just couldn't resist trying.

The attached patch will implement the simpletest hook and add a subdirectory /tests with one testfile that holds two tests:
- create a job setting
- create a job setting and submit an application for that job setting

Keep in mind that I'm still pretty new at Drupal so look out for beginner's faults.

Let me know what you think.

Gr,

Arie