WIP: adapt dynamic feed update scheduling to Sidekiq, replacing Resque-scheduler.
Deleted ScheduledUpdateFeedJob. It has been replaced with a Sidekiq worker.
WIP: adapt tests to the migration from Resque to Sidekiq.

Before testing, stub Sidekiq methods for querying queues, so that they don't attempt to connect to Redis. The fake! method prevents jobs from being actually performed, but unfortunately it does not prevent these methods from attempting to connect to Redis when querying for queues.