Added PayPal Express Checkout, PayPal PayFlow Iframe, PayPal Payments Pro Iframe, Amazon Payments.
Merge pull request #790 from welfordmedia/v1.5.5.1

Payment modules
Merge branch 'v1.5.5.1' of https://github.com/opencart/opencart into v1.5.5.1

Conflicts:
	upload/admin/controller/catalog/product.php
	upload/admin/controller/common/header.php
	upload/admin/controller/sale/order.php
	upload/admin/language/english/common/header.php
	upload/admin/model/sale/order.php
	upload/admin/view/template/catalog/product_form.tpl
	upload/admin/view/template/common/header.tpl
	upload/admin/view/template/sale/order_info.tpl
	upload/catalog/model/checkout/order.php