VID-1958 Dedup the jobs we put into the Task manager


https://wikia-inc.atlassian.net/browse/VID-1958
It does. A task's work id is an sha1 hash of its json representation: https://github.com/Wikia/app/blob/dev/includes/wikia/tasks/AsyncTaskList.class.php#L211 https://github.com/Wikia/app/blob/dev/includes/wikia/tasks/AsyncTaskList.class.php#L276