User Story 6, Users cannot navigate to certain paths

[iandouglas]

Users should see a 404 error under the following conditions:
- if visitors try to navigate to any /profile path
- if visitors try to navigate to any /dashboard path
- if visitors try to navigate to any /admin path
- if registered users try to navigate to any /dashboard path
- if registered users try to navigate to any /admin path
- if merchants try to navigate to any /profile path
- if merchants try to navigate to any /admin path
- if merchants try to navigate to any /cart path
- if admin users try to navigate to any /profile path
- if admin users try to navigate to any /dashboard path
- if admin users try to navigate to any /cart path

If you think of any additional pages to block, please do so.

DO THESE STORIES FIRST:

• User Story 2, Visitor Navigation
• User Story 3, User Navigation
• User Story 4, Merchant 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

depends on #122

depends on #121

depends on #120