Mailers now require a from address, so we need to give defaults, using MailMethod.current

Conflicts:
	api/spec/controllers/spree/api/v1/shipments_controller_spec.rb
	core/app/models/spree/app_configuration.rb
Truncate product description when used as meta description

Fixes #2396

Conflicts:
	core/spec/helpers/base_helper_spec.rb
Correct MailMethod usage in mail_interceptor, order mailer and shipment mailer specs
Don't require payment methods if payment isn't required