When importing an OPML file, the new Sidekiq ImportSubscriptionsWorker is enqueued, instead of the deprecated Resque job.
Fixed log messages
Minor change in comment
When a user requests a feed refresh, a sidekiq RefreshFeedJobWorker is enqueued, instead of the deprecated Resque job.
Added TODO comments to those places in which scheduling is managed.

We'll have to migrate from resque-scheduler to another system that is compatible with Sidekiq. Sidekiq wiki suggests Clockwork, Whenever, Sidekiq-cron or Sidetiq as possible solutions:

https://github.com/mperham/sidekiq/wiki/Scheduled-Jobs

When one of these solutions is adopted, all that code that references Resque-scheduler will have to be updated.
Fix comment
When enqueuing a subscribe job as part of an OPML import or when a user adds a subscription, the new Sidekiq worker is enqueued instead of the deprecated Resque job.
Reworked tests to account for the fact that the Sidekiq worker SubscribeUserWorker has replaced the deprecated Resque job.
When unsubscribing from a feed, the sidekiq UnsubscribeUserWorker is enqueued, instead of the deprecated Resque job.
When multiple entries are marked as read, the sidekiq UpdateFeedUnreadCountWorker is enqueued, instead of the deprecated Resque job.