Added support for installing packages conforming to PSR-4 standard
Fixes #1827: Debugger toolbar is loaded twice if an action is calling `run()` to execute another action
Fixes #1835: `CheckboxColumn` now renders checkboxes whose values are the corresponding data key values
updated extension changelog.
default values for db\Connection username and password to null

fixes #1821
Advanced app template: moved database connection DSN, login and password to -local config not to expose it to VCS
Adjusted advanced application template docs to reflect DB config movement
Added readme line for advanced app change
Fixes #1633: fixed scenarios for User model in advanced application allowing setting default values for User model
Added link to ICU Locale docs in order to clarify what are Yii::$app->language values
Removed translations for messages intended for developers
Improved plural messages for validators
Added guide for contributing message translations
Added message translations for Russian
Fixes #1846
Fixes #1820: Update Progress to use bootstrap 3 markup
Add pt-BR translated messages
Fixed production environment for advanced app
Merge pull request #1848 from alanwillms/pt-br-messages

Add pt-BR translated messages
Removed error-block HTML class and related styles and used Bootstrap3 standard practice about errors instead