Fixes #2653: Fixed the bug that unsetting an unpopulated AR relation would trigger exception (qiangxue)

Fixes #2603: `yii\base\ErrorHandler` now extends `\ErrorHandler`

RESTful API support

Add size attribute to Modal

Conflicts:
	framework/db/BaseActiveRecord.php

Removed U+FEFF character from pt-PT language file to fixe #2631

This reverts commit 2bb6f135.

`User` here

Keyboard shortcut for previous, next and refresh buttons

fixes #2632

We are now maintaining a fork of pjax:
https://github.com/yiisoft/jquery-pjax

apps code style fixes

* 'master' of github.com:yiisoft/yii2: (40 commits)
  Fixes #2624: Html::textArea() should respect "name" option.
  Removed unused "use" statements
  Changed "and" to "&&"
  Used ternary operator instead of "or" for constant definition
  Removed unused variables
  Removed executable flag from asset files
  Changelog for #2607
  Added note about overriding asset bundles according to #2556
  Added some documentation to new pjax attribute
  Add unit tests
  typo fix.
  Update MessageController.php
  Update MessageController.php
  add findAndModify() method to the Collection class
  Add an option to ignore pjax request on some links.
  fix code style php5.4 syntax
  Inline control structures are not allowed
  fix code style
  fix code style
  fix typo double `;`, `Each PHP statement must be on a line by itself`
  ...

fixes #2623