Replace ApiTestCase with PHPUnit_Framework_TestCase

- Move to `SMW\MediaWiki\Api` NS
- Replace `ApiTestCase` with `PHPUnit_Framework_TestCase` and remove ` ApiTestCase`
- Access to MediaWiki's `Api` during test is enabled through `SMW\Tests\Util\MwApiFactory`
- Add `SMW\Application` for external and internal instance access
- Add `SMW\MediaWiki\Jobs\JobFactory` which is accessible via `SMW\Application::getInstance()->newJobFactory()` to avoid having third-party developers wire up SMW internal objects directly.
- `SMW\Application` is introduced with this PR to gain access to the `SerializerFactory` & `Wikipage:Factory` object while allowing to mock those objects during the test.

```php
Application::getInstance()->getStore()
Application::getInstance()->newSerializerFactory()
Application::getInstance()->newWikiPage()
Application::getInstance()->newJobFactory()
```
Since you end up having no logic in the API modules, you don't really need to test them. Some smoke test or simple system test works, and for those you do not need to mock out the things. In fact, it's nicer if you don't, since if you do, you remove part of the value of having a system test.

I did not quite guess the reasoning behind this code before. If it's for that, and you hold my concerns into account, I'm not against having this.