issue #3494

without check

fixes #3438

breaking changes.

To comply with the docs RE namespace usage:
https://github.com/yiisoft/yii2/blob/master/docs/guide/extend-creating-extensions.md

fixes #3289

do not allow empty property name
fixes #3297

Adding a new additional validation rule in the gii-crud generator enforcing the expected format.

implementation checks for instanceof for additional swiftmailer
capabilities.

issue #2870