Merge pull request #17 from AbrahamGreyson/master

proofread.
Fixes PHPDoc
added common tier config
Unit test for `MigrateController` added
'MongoDbTestCase::loadClassMap()' refactored
Unit test for MongoDB migration controller added
Update UPGRADE.md

fixed indentation
Advanced app `User` model code style fixes
Fix invalid indentation.
Initial migration code must match code generated by console migration controller.

Minor consistency issue. See the following files for more details:
1. framework/views/migration.php
2. framework/console/controllers/MigrateController.php
Fixes #3384: Added callback-style transactions
Fixes #4241: `yii\widgets\Pjax` was incorrectly setting container id
Fixed example of closure-transactions
Fixed tests
Passed transaction as callback argument for Connection::transaction() method
Removed requirement to use \Callback from Connection::transaction, improved docs
Added callable typehint and active transaction check to Connection::transaction()
Added extra callable typehints
Fixed missing callable in method signature
minor CS fixes [skip ci]