Move Spinach setup for db_cleaner and capybara to their own files

Also adds capybara-screenshot, which will automatically save the page as
html and an image whenever a feature fails. Handy for debugging.

features/support/capybara.rb

+require 'spinach/capybara'
+require 'capybara/poltergeist'
+
+Capybara.javascript_driver = :poltergeist
+Capybara.register_driver :poltergeist do |app|
+  Capybara::Poltergeist::Driver.new(app, js_errors: false, timeout: 90)
+end
+
+Spinach.hooks.on_tag("javascript") do
+  Capybara.current_driver = Capybara.javascript_driver
+end
+
+Capybara.default_wait_time = 60
+Capybara.ignore_hidden_elements = false
+
+require 'capybara-screenshot/spinach'
+
+# Keep only the screenshots generated from the last failing test suite
+Capybara::Screenshot.prune_strategy = :keep_last_run

features/support/db_cleaner.rb

+require 'database_cleaner'
+
+DatabaseCleaner.strategy = :truncation
+
+Spinach.hooks.before_scenario do
+  DatabaseCleaner.start
+end
+
+Spinach.hooks.after_scenario do
+  DatabaseCleaner.clean
+end

features/support/env.rb

@@ -11,40 +11,18 @@ ENV['RAILS_ENV'] = 'test'
 require './config/environment'
 require 'rspec'
 require 'rspec/expectations'
-require 'database_cleaner'
-require 'spinach/capybara'
 require 'sidekiq/testing/inline'
 
+require_relative 'capybara'
+require_relative 'db_cleaner'
+
 %w(select2_helper test_env repo_helpers).each do |f|
   require Rails.root.join('spec', 'support', f)
 end
 
-Dir["#{Rails.root}/features/steps/shared/*.rb"].each {|file| require file}
+Dir["#{Rails.root}/features/steps/shared/*.rb"].each { |file| require file }
 
 WebMock.allow_net_connect!
-#
-# JS driver
-#
-require 'capybara/poltergeist'
-Capybara.javascript_driver = :poltergeist
-Capybara.register_driver :poltergeist do |app|
-  Capybara::Poltergeist::Driver.new(app, js_errors: false, timeout: 90)
-end
-Spinach.hooks.on_tag("javascript") do
-  ::Capybara.current_driver = ::Capybara.javascript_driver
-end
-Capybara.default_wait_time = 60
-Capybara.ignore_hidden_elements = false
-
-DatabaseCleaner.strategy = :truncation
-
-Spinach.hooks.before_scenario do
-  DatabaseCleaner.start
-end
-
-Spinach.hooks.after_scenario do
-  DatabaseCleaner.clean
-end
 
 Spinach.hooks.before_run do
   include RSpec::Mocks::ExampleMethods