Fixes #2932: Added `yii\web\ViewAction` that allow you to render views based on GET parameter
Renamed basePath to viewPrefix
Dropped defaultView
Extracted render method to allow custom renderers by subclassing
Removed ViewAction::afterRun()
Merge pull request #2934 from yiisoft/action-for-static-pages

Fixes #2932: Added `yii\web\ViewAction` that allow you to render views based on GET parameter
Refactored ViewAction.