Fix Buzz integration tests

* Namespaced `tests/` dir
* Included `phpunit.xml.dist` file
* `setup()` and `teardown()` methods should be protected in tests
* Created `tests\AlgoliaSearch\Tests\AlgoliaTestCase` that includes functions from old `tests/helper.php` file and extends `PHPUnit_Framework_TestCase`
* Removed `tests/helper.php` in favor of `AlgoliaTestCase` class
* Include use statements for `AlgoliaSearch\Client` and `AlgoliaSearch\AlgoliaException`
* Moved test class fields to head of class code body