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()
```
Not a fan of this. I much prefer immediately breaking of of the API context by fetching an object handling the request from the top level factory.

Examples:

* https://github.com/wmde/WikibaseQuery/blob/master/src/Api/EntitiesByPropertyValue.php#L43
* https://github.com/JeroenDeDauw/Wikibase/blob/299d39fc76d2e9ca1ddac4fe57d203fd00d42dfc/repo/includes/api/CreateRedirect.php#L34-L35

When doing this, there is little point in having this code.