Advanced app: Username should be unique

Really not sure what this is. It seems incomplete as is.

issue #1797

Fixes #2629: `Module::controllerPath` is now read only, and all controller classes must be namespaced under `Module::controllerNamespace`

Apidoc refactoring

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

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

* master: (153 commits)
  rest doc.
  CS fix
  Add size attribute to Modal
  major features and documentation finished for REST API.
  rest WIP
  Removed U+FEFF character from pt-PT language file to fixe #2631
  Revert "Used ternary operator instead of "or" for constant definition"
  `User` here
  REST wip.
  Changelog
  reset access cache when user identity is set
  Keyboard shortcut for previous, next and refresh buttons
  reset batch query result when rewinding.
  fixed loading namespaceless controller classes.
  Fixes #1467: Added support for organizing controllers in subdirectories
  replace pjax with external resouce via composer
  fixed > 100 typos introduced by me :-)
  fixed condition for HHVM test
  fixed phpdoc
  updated phpdoc references of BaseAR to the interface
  ...

Conflicts:
	extensions/apidoc/templates/BaseRenderer.php
	extensions/apidoc/templates/html/views/constSummary.php
	extensions/apidoc/templates/html/views/propertyDetails.php

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