Feature/enqueue now

@bavndenbos, I've been using my fork in production for the past 9 months successfully, enqueuing thousands of future-jobs per day. Here are some small modifications that make a lot of sense:

* When assigning the schedule, set, don't append
* If you try to enqueue_at in the past, it just enqueues now. No point in using a middleman here
* Add the server local time to resque-web