Remove APScheduler, it is no longer used by Mayan EDMS
Issue #57, convert installation app to use celery
Add retry and rate limit support to the installation task
Issue #57, update the registration app to use Celery
Pass task configuration to the decorator, not to the task itself
Add the bing argument to enable .self access
Improve registration view workflow now that a queued task is used
Set the ignore_result option for the tasks that don't return values