[web] Show sidebars inline in ChatThreadList

Summary: Just like on native in this video: https://site.ashoat.com/comm/app/demo

Test Plan: Look at the sidebars on my web environment, make sure pressing them brings up the ChatMessageList

Reviewers: KatPo, palys-swm

Reviewed By: KatPo, palys-swm

Subscribers: zrebcu411, Adrian

Differential Revision: https://phabricator.ashoat.com/D461