Add absoluteAuthTimeout to yii\web\User.

This is based on the code from Yii 1.1.14 by Ivo Kund.
update changelog for 4317
Merge branch 'master' of git://github.com/yiisoft/yii2 into 4317-absolute-auth-timeout

Conflicts:
	framework/CHANGELOG.md
Merge pull request #4325 from nkovacs/4317-absolute-auth-timeout

absolute auth timeout
Fixes #4318: `yii\helpers\Html::ul()` and `ol()` will return an empty list tag if an empty item array is given
`yii\mongodb\log\MongoDbTarget` log target added
Fixes #4310: code cleanup
Fixes #4295: reworked message extraction for PO files
gii: fixed wrong composer.json template

reverts 45e4973ac80d4291dbc5cf321a088457b295d361
improved docs about goBack()

fixes #4343
Fixes #4331: `yii\helpers\Url` now uses `UrlManager` to determine base URL when generating URLs
Fixed test break.
Fixes #3443: Fixed `yii\bootstrap\Nav` and `yii\bootstrap\Dropdown` were generating wrong ids for submenus
Passed "encodeLabels" to Dropdown recursive call