Fixes #4122: `Html::error()` and `Html::errorSummary()` are now accepting `encode` option. If set to false it prevents encoding of error messages

Improved checks where substr_compare is used, replaced more substr + comapre cases with substr_compare

fixes #4105, close #4376

Fixes #4318: `yii\helpers\Html::ul()` and `ol()` will return an empty list tag if an empty item array is given

Fixes #3358: Removed automatic CSRF meta tag generation by `View`. Added `Html::csrfMetaTags()` and its call to main layout files

No changelog line since feature was introduced after beta

Fixes #2906: Added support for using conditional comments for js and css files registered through asset bundles and Html helper

issue #2852