[web] Move activeTab control to provider

Summary: This diff moves activeTab control to ThreadListProvider, so we can handle switching tabs and getting threadList in one place, instead having this logic split between ChatTabs and provider

Test Plan: Flow and checking if nothing changed when switching tabs, this is mostly refactoring

Reviewers: palys-swm, ashoat

Reviewed By: palys-swm, ashoat

Subscribers: ashoat, palys-swm, Adrian, atul

Differential Revision: https://phabricator.ashoat.com/D1035