RBAC: Item and Assignment optimized save approach

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.

issue #237

https://github.com/yiisoft/yii2/commit/e2513de6c6207fa37894a944e10b8cd420ac6804#commitcomment-3192244

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

as discussed in #203
https://github.com/yiisoft/yii2/issues/203#issuecomment-17759631

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

RBAC: DbManager code style

change is to avoid random test failure on race condition.
fixes #203 #231

Merge pull request #204 branch 'unittest-app-dependency' of https://github.com/bwoester/yii2 into bwoester-unittest-app-dependency

* 'unittest-app-dependency' of https://github.com/bwoester/yii2:
  mod: incorporate suggestions - rename requireApp() to mockApplication() - always destroy app on tearDown()   - eliminates need for constant YII_DESTROY_APP_ON_TEARDOWN   - mockApplication() becomes a lot easier. Destroying app on each tearDown     means creating it on every call is fine. No more checking if it already     exists and if it has been created from the same config. - \yii::$app should have been \Yii::$app
  add: new key for unit tests config named "className". Allows to run the tests      using different Application instances (consoleApp/ webApp) mod: TestCase::getParam accepts second param $default=null
  mod: don't create app in bootstrap script, unit tests do it themselves add: option to destroy app after each test to find unit tests that fail      to require an app
  allow unit tests to requireApp() on setUp()

Conflicts:
	tests/unit/data/config.php