also changed PHP Intl support to optional.

Renamed yiirequirements.php to requirements.php

"YiiRequirementChecker" console view has been reworked to display requirements by blocks and in brief for the successful ones.

Yii core requirements file has been composed.

"YiiRequirementChecker::check()" has been updated to be able to collect different requirements set in the chained call.

Methods "YiiRequirementChecker::getResults()" and "YiiRequirementChecker::render()" have been added.