User Story 21, (EXTENSION 1/4) User reviews are sortable

[BrianZanti]

As a Visitor,
When I visit a user's show page to see their reviews,
I see additional links to sort their reviews in the following ways:
- sort reviews by highest rating, then by descending date
- sort reviews by lowest rating, then by ascending date

DO THESE STORIES FIRST:

• User Story 16, User Show Page

Checklist:

• base code tests are written
• base code is written to pass tests
• edge case ("sad path") tests written
• edge case code written
• code is reviewed
• branch is merged
• all tests still pass

child of #5

child of #33

depends on #11