Revert "check for class existence, and log when it's not found"

This reverts commit df1563ce2f247defacbf863b485c999a0e34763a.
allow global context/field objects to get into log messages, and change db_name, wiki_id, etc to add themselves via this mechanism. also update task_runner.php to add the current task_id this way, so fatals/warnings/notices that tasks generate will show up in a task's log
changing return types and php docs
Merge remote-tracking branch 'origin/dev' into logging-context

Conflicts:
	includes/wikia/tasks/Tasks/BaseTask.class.php
Merge pull request #3934 from Wikia/logging-context

Logging context