Correct documentation for title helper

Fixes #2878

Conflicts:
	core/lib/spree/core/controller_helpers/common.rb
Only set ActiveMerchant::Billing::Base if gateway_options[:server] is available
Bump highline to 1.6.18
Bump ffaker to 1.15.0

This will fix a bundle conflict when I switch between 1-3-stable and master branches.
Replace tabs with spaces in config/routes.rb
Remove executable bit from core/config/routes.rb
Add missing back_to_users_list to core/config/locales/en.yml