Closing and opening braces in Yii2 coding standards.

Further coding standards fixes.

Didn’t touch the end yet, with the TBD et al.

Coding standards fixes.

nulls in batchInsert. Patch available.

Add getIsPjax method to Request, and add X-PJAX-URL header when redirect from pjax request

Fixes #2392: Added `addCssStyle()`, `removeCssStyle()`, `cssStyleFromArray()` and `cssStyleToArray()` to `Html`

Allow add a condition telling the table to avoid ambiguity error.

fixes #2519: MessageSource removed translation messages when event handler
was bound to `missingTranslation`-event

Fixes #2491: Added support for using the same base class name of search model and data model in Gii [skip ci]