`yii\console\controllers\AssetController` now correctly handles relative image URLs if source and target CSS are under same directory

fixes #6691

Fixes #5627: Added `yii cache/flush-schema` console command to flush DB schema cache of a given database connection

Fixes #5504: Added note to yii\console\CacheController explaining that cache components should be configured in console app configuration in order to be cleared

Fixes #4823 and #6005: `yii message` accuracy and error handling were improved by using PHP tokenizer instead of regular expressions. Removed eval() as well.

Fixes #6107 and #6112: `yii message` was emptying existing translations and incorrectly writing not yet translated strings in .po in case of multiple categories

Fixes #5954: `yii message` command now shows user friendly error if it's not able to parse source file

Fixes #5682: The `asset` command would incorrectly combine CSS files when `UrlManager::linkAssets` is true

before: failed with undefined index PHP error
now: fail with proper error complaining about missing argument.

API is not finished.

issue #5082

Fixed `yii\console\controllers\AssetController` breaks CSS URLs in case target file localed at `yii\web\AssetManager::basePath` root

fixes #5342