User Story 25, Visitors must register or log in to check out

[memcmahon]

As a visitor
When I have items in my cart
And I visit my cart
I see information telling me I must register or log in to finish the checkout process
The word "register" is a link to the registration page
The words "log in" is a link to the login page

DO THESE STORIES FIRST:

• User Story 21, User views their cart show page with items in the cart
• User Story 2, Visitor Navigation
• User Story 7, User Registration
• User Story 10, User can Login

Checklist:

• base tests are written
• base code is written to pass tests
• edge case ("sad path") tests written (if required)
• edge case code written (if required)
• code is reviewed
• branch is merged
• all tests still pass

child of turingschool-projects#249

child of turingschool-projects#274

depends on turingschool-projects#247

depends on turingschool-projects#271

depends on turingschool-projects#265

depends on turingschool-projects#261