Extract Capybara setup to a helper file

Any Capybara-related test setup has been moved to `capybara_helper.rb`.
Now we just must require this file in order to run tests with Capybara.

I also moved the `#console_log` helper to this file to showcase how
other global helper methods could be defined in this file.

test/capybara_helper.rb

@@ -0,0 +1,21 @@
+require_relative 'helper'
+
+require 'selenium-webdriver'
+require 'capybara/dsl'
+
+CAPYBARA_DRIVER =
+  if ENV['CI']
+    :selenium_chrome_headless
+  else
+    ENV.fetch('CAPYBARA_DRIVER', :selenium_chrome).to_sym
+  end
+
+Capybara.default_driver = CAPYBARA_DRIVER
+Capybara.enable_aria_label = true
+Capybara.server = :webrick
+
+def console_log(page, level = :severe)
+  page.driver.browser.logs.get(:browser).select { |log| log.level == level.to_s.upcase }
+end
+
+