Add sidekiq monitoring web interface

www.agileplannerapp.com/boards/173808/cards/5259

this web application exposed at '/sidekiq' allows
us to monitor queue state and manage messages.
Merge pull request #243 from alphagov/sidekiq-monitoring

Add sidekiq monitoring web interface
Always include detail message in health check.

There's no harm including this, it's handy to be able to see how many
publications are queued, and it simplifies the code.
Merge pull request #244 from alphagov/always-show-message

Always include detail message in health check