Allow coupon code with special charater to be applied to order in checkout

[gabrielqs-redstage]

Fixes issue where coupon with special char (ex: %) could not be applied to quote in checkout, payment step

Description

Encoding of coupon code prior to requesting it to be applied

Fixed Issues (if relevant)

1. When go checkout,Cart Price Rules 25%test coupon code can go wrong #9763: When go checkout,Cart Price Rules 25%test coupon code can go wrong

Manual testing scenarios

1. In the admin, create a shopping cart price rule, and set it to use a coupon code, specify the coupon code to be 25%off. Set very broad conditions - preferably none - select all websites and all user groups.
2. In the frontend, add a product to cart
3. Proceed to checkout, type in address and select shipping method. It makes no difference if you're logged in as a customer or not
4. Proceed to the payment method step and apply the coupon code 25%off. The coupon code will be applied correctly

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)