User Story 4, Merchant Navigation

[memcmahon]

As a merchant user
I see the same links as a visitor
Plus the following links:
- a link to my merchant dashboard ("/dashboard")
- a link to log out ("/logout")

Minus the following links/info:
- I do not see a link to log in or register
- a link to my shopping cart ("/cart") or count of cart items

DO THESE STORIES FIRST:

• User Story 3, User Navigation

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#272

child of turingschool-projects#274

depends on turingschool-projects#270