MigrateCommand enhancement. `all` option added for `down` action.
CHANGELOG updated
Comments updated
CHANGELOG fixed
MigrateController refactoring
Merge PR #3421 branch 'migrate-command-enhancement' of https://github.com/creocoder/yii2

* '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