Use real buttons for reading and writing reviews

Right now the way you access the sheets to read and write reviews is to
click on link buttons in odd places, which suffer from various minor
issues:
- Typically underlined link text opens a URL, not another page in the UI
- Link buttons are very small and can be missed when they're in a rich
  page layout
- The "show all reviews" link is at the top of the reviews section, not
  at the bottom where you would expect it (the flow is look at the
  three top reviews -> want to see more, which means that it should be
  below the three top reviews, not above)

This commit addresses those issues by making the buttons into real
Buttons and placing them both in a row below the three top reviews.