Remove spork

Spork interferes with debugging as the pry console is sent to the spork
process which competes for input with the guard terminal.
Remove `require_tree ./helpers`

Currently no helpers exist so a clean checkout of the application will
error because `app/assets/javascripts/helpers` does not exist.
Use pry in test and development
Change role factories to traits
Set Delivery#delivered_on in factories
Ignore hidden elements in capybara

Encourages assertions that better mimic the end-user's experience by not
being able to interact with hidden elements.
Port turnip features to plain rspec