[web] Only bold unread thread titles

Summary: This is more consistent with native and makes it clearer which threads are unread.

Test Plan: Look at the website on my local dev environment

Reviewers: KatPo, palys-swm

Reviewed By: KatPo, palys-swm

Subscribers: zrebcu411, Adrian

Differential Revision: https://phabricator.ashoat.com/D460