Sidekiq now has the same queues (subscriptions, update_feeds, maintenance) that Resque had.

Queues are also weighted so that more critical workers are checked more often. This seems superior to Resque, in which worker processes were assigned a single queue.
Added sidekiq web ui under the /sidekiq path.

The web ui is currently unauthenticated, unauthorized.

See: https://github.com/mperham/sidekiq/wiki/Monitoring
Added unit test for CleanupInvitationsWorker (the only resque job converted to sidekiq worker, for the moment).
Show link to sidekiq web ui in the user menu.

For the moment everyone sees the link. Obviously we will want to show it only to admins, and furthermore to restrict URL access to authenticated admins.
Restrict access to the sidekiq web ui to authenticated admin users.