Revert "[web] [refactor] remove unneeded div in chat-thread-list component"

Summary:
This reverts commit 8de95514f0a0213981e4cb9f790bc3393c4c3930.

before:

Test Plan: this broke web. The mark as read button is now showing when there isn't a hover over the chat thread item element.

Reviewers: atul

Reviewed By: atul

Subscribers: ashoat, palys-swm, Adrian, karol-bisztyga

Differential Revision: https://phabricator.ashoat.com/D3407