issue #3494

* 'exist-validator-enhancement' of https://github.com/creocoder/yii2:
  ExistValidator final refactoring. `allowArray` checking also added to `validateValue` method.
  New tests added
  New tests added
  ExistValidator::validateValue() fixed
  Tests excess dump removed
  ExistValidator bugfix
  Tests updated
  ExistValidator refactoring
  CHANGELOG updated
  `allowArray` introduced.
  CHANGELOG
  ExistValidator count logic fix
  Tests updated
  Tests updated
  Tests updated
  Refactoring
  Refactoring
  Improve `exist` validator to support array attributes

Conflicts:
	framework/CHANGELOG.md

simple fix #3461

Control checkbox in the preview window.

without check

Revert "Fixes #3469: Fixed the bug that `QueryBuilder::getColumnType()` may drop the provided column precision in certain cases"

This reverts commit a46efe79.

This reverts commit 70b57766.

Fixes #3469: Fixed the bug that `QueryBuilder::getColumnType()` may drop the provided column precision in certain cases

* 'migrate-command-enhancement' of https://github.com/creocoder/yii2:
  MigrateController refactoring
  CHANGELOG fixed
  Comments updated
  CHANGELOG updated
  MigrateCommand enhancement. `all` option added for `down` action.

Conflicts:
	framework/CHANGELOG.md

Update various typos and grammar

Small changes according to the class reference

[travis-ci] Allow fast finishing

It looks like this values are supposed to be in different order due to the class reference and practice.

Fixes #3458: Fixed the bug that the image rendered by `CaptchaAction` was using a wrong content type

changed comments #3446