sub menus didn't get checked for being active.

Based off the method in ```Menu.php``` I've updated ```Nav``` so it will check if sub menus are active or not.
Improved check for active child items

Updated to avoid full tree traversal.
Also noticed ```activateItems``` didn't do anything so that's been fixed.
Update CHANGELOG.md
Added asElapsedTime function
Typo in asElapsedTime description
Call Yii::t everytime instead of passing a template variable
Typo
asElapsedTime can now take DateInterval as parameter
asElapsedTime style improvements
asElapsedTime can now take a DateInterval string as a parameter
Added support for inverted intervals (future time) and unit tests
Removed debug code, changed doc
Modified example in DataReader usage comment to reference a DB Command function which accepts a SQL string argument.
GII generated files changes according to PSR2
Merge pull request #2771 from lucianobaraglia/gii-psr2

GII generated files changes according to PSR2
upd for psr2
Added return value for User::logout().
Merge branch 'master' of git://github.com/yiisoft/yii2 into fix-gridview-url
fix
changelog