Move "Viewed" checkbox to the bottom of the file (or add another there)

[tadeu]

The "Viewed" checkbox is a nice recent addition to GitHub PR's, but it is annoyingly located at the top of the file. We usually read files from top to bottom, so the most natural location would be at the bottom (to avoid scrolling, etc., just read the file and check it)

[fregante]

File headers are sticky so you'll always have that on screen for the entirety of the file. You never have to scroll to see it.

[tadeu]

True, I noticed this just right after creating this issue 😅🤦‍♂