Use SMW\MediaWiki\Jobs\...

- Use SMW\MediaWiki\Jobs\ namespace
- Use PHPUnit_Framework_TestCase
- Modify some tests to be a bit more expressive
- Make Job::getType accessible for MW 1.19 / MW 1.20

Change-Id: If7a9eb3462ff50ec26e9232b07f6dbadfba7a00b