Move env-specific bits to the engine

[jorgemanrubia]

See basecamp/fizzy-saas#10

[jorgemanrubia]

This is tested and ready to go. I will deploy later.

[flavorjones]

I think we should also add to fizzy-saas:

# config/environments/development.rb
  if Rails.root.join("tmp/solid-queue.txt").exist?
    config.solid_queue.connects_to = { database: { writing: :queue, reading: :queue } }
  end

and remove that line from the application config. (Because the queue database does not exist in the OSS database configs.)

[jorgemanrubia]

👍 moved here and here.