Line should always appear when user scroll down

[jkup]

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Ran git rebase -i to squash commits (if needed).

Fix #3888

Auditors: @bradleyrichter @diracdeltas @bbondy

Test Plan:

If you have enough publishers to cause a scroll, the headers (Rank, site, Include, etc) should remain fixed to the top)

This is the only way I could figure out getting it to work without JavaScript. It's kind of ugly. Let me know if the code is worth the feature or if any of you know a better way!

[diracdeltas]

could you please rebase this?

[jkup]

Realizing while rebasing this isn't exactly what we want. We want only this one particular table to be fixed headers, not all sortable tables. Since this doesn't seem pressing for 0.12.2 -- is it cool if I just bump this to 0.12.3 and grab it this week? + @bbondy @diracdeltas

[diracdeltas]

i'm ok with bumping this

[jkup]

Closing for now, will open a new PR with the new approach.