Consider making scheduled jobs optional

[JustinLove]

@espen

I suggest that there is a value to be set which specifies timeframe for the autoscaler to stay idle if there are scheduled jobs.

I.e.: :schedule_limit => 5.minutes. will cause autoscaler to scale down if the next scheduled jobs is 10 minutes from now and to stay idle if the next job is 4 minutes from now.

Scheduled jobs must then either be processed whenever autoscaler scales up again or through Heroku Scheduler.

[JustinLove]

Scaling strategies will be available in 0.4.0