User Story 58, Admin is redirected from User profile to Merchant dashboard

[memcmahon]

As an admin user
If I visit a profile page for a user, but that user is a merchant
Then I am redirected to the appropriate merchant dashboard page.
eg, if I visit "/admin/users/7" but that user is a merchant
Then I am redirected to "/admin/merchants/7"
And I see their merchant dashboard page

DO THESE STORIES FIRST:

• User Story 56, Admin User Profile Page
• User Story 38, Admin can see a merchant's dashboard

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 #208

child of #274

depends on #206

depends on #228