Actualize phpunit usage approach

1) Yii 2 unit tests is not worked if using `phpunit.phar`
2) Since we are composer guys its better to have `phpunit` under `require-dev` section as recommended at http://phpunit.de/manual/3.7/en/installation.html
3) PEAR is dead a long time ago

After merge there is two ways to run tests:

1) Download `phpunit.phar` and run it
2) `composer update` and run `./vendor/bin/phpunit`