User Story 38, Admin can see a merchant's dashboard

[BrianZanti]

As an admin user
When I visit the merchant index page ("/merchants")
And I click on a merchant's name,
Then my URI route should be ("/admin/merchants/6")
Then I see everything that merchant would see

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 #233

child of #274