Add Devel Debug Log

[olofbokedal]

Awesome module which makes debugging during AJAX requests, drush commands, batch operations easier - https://www.drupal.org/project/devel_debug_log

Have experienced some problems for D8 though so we might need to include some patches based on open issues. We also need to make sure that devel or debug information isn't exposed automatically, it should be enabled (or similar) via settings.php.

(Copied from oddhill/drupal-starter-kit#12)