Fixes #2726: ActiveRecord now fills default values on creating new instance of the model if defaults are available from DB schema

Changed comment again to actually be correct. This is also consistent with the draft of the definitive guide.

Modified example in DataReader usage comment to reference a DB Command function which accepts a SQL string argument.

Changed comment again to actually be correct. This is also consistent with the draft of the definitive guide.

{max} was used instead of {min} in the error message for the min validator...

Fixes #2775: Added `yii\base\Application::bootstrap` to support running bootstrap classes when starting an application