Solid queue

Migrate from sidekiq to solid_queue. The main reason for the migration is connected with unique jobs, available in Sidekiq Pro but not in the community version. I'm aware of https://github.com/mhenrixon/sidekiq-unique-jobs but it does not play nicely with active jobs we are using.

TODOs:

• to solid queue
• use mission control to show job statuses
• use recurring jobs instead of clock (eliminate this dependency)
• fine-tune solid queue configuration (number of workers, priorities, etc.)

Maybe not in this MR:

• unique jobs for updating job statuses

Remarks:

• AdminApplicationController was added to check if user is an admin (and redirect back if not). It is used as a base class for the mission_controll-jobs. Thanks to this configuration I was able to eliminate User.find_by during the routes initialization (made in every root request).
• admin/jobs has no application layout right now - it is possible to add a layout but I don't see a point for it since this view is only for internal ("MEE root" level) usage.