Moved debug toggle from AppKernel to web/app_dev.php

`AppKernel->init()` was using deprecated classes and was duplicating code and is deprecated itself altogether. So moved code to where it belongs - app_dev.php.

https://github.com/symfony/symfony-standard/blob/master/app/AppKernel.php
https://github.com/symfony/symfony-standard/blob/master/web/app_dev.php

Also removed `ini_set('date.time', 'UTC');` as should be already set in php.ini depending on server location (plus we have that set in puppet script):

https://github.com/Im0rtality/Sylius/blob/master/vagrant/manifests/default.pp#L118

Solves some SensioInsight major warnings.

This partially overlaps with #513, but last commit was 3 months ago.