proofread intro-yii.md and intro-upgrade-from-v1.md

Update BaseMessage.php

See https://github.com/yiisoft/yii2/commit/0ff0f9d32eb71cc13b7c6eea45f85d115f98a633

https://github.com/yiisoft/yii2/issues/4071

Fix #87: security helper converted into component and improved

Chinese Translation for this week

* upstream/master:
  Reverted #4098.
  fix duplicated white space and typo [skip ci]
  typo fix
  Fixes #4098: `yii\db\Query::addSelect()` should include `*` when it is called the first time

fix duplicated white space and typo [skip ci]

* upstream/master:
  typo fixes [skip ci]

Upgrade Bootstrap from 3.1 to 3.2

Fix json format in gii/generators/extension/default

* upstream/master:
  resolved naming conflict in apidoc