Add a "new comment" indicator to cells

[cameron-toy]

Add some sort of indication that a comment/new comment exists on a comment target.

In @chloefrerichs mock-up below, the indicator exists as an orange circle (which is supposed to be a stand-in for the user's profile picture)

Clicking the indicator should open the comments panel and scroll to that comment. In the future, this may be replaced with an in-line comment widget.

[srirag-vuppala]

Implemented in previous PRs

[nairrrahul]

Re-Opened