Fix https://gitlab.com/gitlab-org/gitlab-ee/issues/4474

Conflicts:
	db/schema.rb
	ee/app/controllers/ee/admin/application_settings_controller.rb
	ee/app/helpers/ee/application_settings_helper.rb
	ee/app/models/ee/application_setting.rb
	ee/app/models/license.rb
	ee/app/views/layouts/service_desk.html.haml
	ee/app/views/notify/approved_merge_request_email.html.haml
	ee/app/views/notify/service_desk_new_note_email.text.erb
	ee/app/views/notify/service_desk_thank_you_email.text.erb
	ee/app/views/notify/unapproved_merge_request_email.html.haml
	ee/lib/ee/api/entities.rb
	ee/spec/controllers/admin/application_settings_controller_spec.rb
	ee/spec/models/application_setting_spec.rb
	ee/spec/requests/api/settings_spec.rb
	lib/api/settings.rb
	spec/mailers/previews/notify_preview.rb