Make project show page more compact

The project show page had started to grow out of control when more and
more snapshots were added. Instead of showing all snapshots for each
url/viewport pair, we now only show two. To see all snapshots, you have
to go to the url show page (added in this commit).
Add "View all" link to snapshot boxes

On the project show page we now only list two snapshots for each
viewport. To get quick access to all snapshots, I added a 'View all'
link that takes you to the url show page (anchored to the correct
viewport block).