User Story 8, Item Show

[BrianZanti]

As a visitor
When I visit '/items/:id'
Then I see the item with that id including the item's:
- name
- active/inactive status
- price
- description
- image
- inventory
- the name of the merchant that sells the item

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 tested in development
• code is reviewed
• branch is merged
• all tests still pass

child of #32

child of #39