Fixes #1856: The default CSS class for hint generated by `ActiveField` is changed to `help-block`
Revert "Fixes #1856: The default CSS class for hint generated by `ActiveField` is changed to `help-block`"

This reverts commit 7ae4695d0cf46f3347ff8f340f572a08419f21a7.
docs added
tests improved
code fix
tests improved
CS fix.
Merge branch 'master' of github.com:yiisoft/yii2-app-basic