User Story 63, EXTENSION: Admin cancels a user's order

[BrianZanti]

As an admin user
When I visit a user's order show page
If the order is still "pending", I see a button or link to cancel the order
When I click the cancel button for an order
The same behaviors happen as if the user canceled the order themselves

DO THESE STORIES FIRST:

• User Story 17, User Profile Show Page
• User Story 29, User views an Order Show Page

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 #201

child of #274

depends on #252

depends on #238