Fixes #1535: Improved `yii\web\User` to start session only when needed. Also prepared it for use without session.

Fixes #1564: Removed `yii\web\Session::autoStart` and added `hasSessionId`. Session will be automatically started when accessing session data

for prev, next, first and last page.
http://www.w3.org/TR/html401/struct/links.html#h-12.1.2

Changed `Controller::afterAction()`, `Module::afterAction()` and `ActionFilter::afterAction()` to pass `$result` by value instead of reference

Enable IDE typehints for custom AssetBundle properties (related to #2572).

call hasMethod() instead of using method_exists

Fixed typo in runWithParams

Fixes #2544: Changed `DetailView`'s `name:format:label` to `attribute:format:label` to match `GridView`

added a missing argument

Fixes #2527: Source language for `app` message category was always `en` no matter which application `sourceLanguage` was used