[web] Switch tab when opening sidebars

Summary:
When sidebar is a child of thread from chat list, we need to switch tab if the other one is active. When sidebar is a child of non-member thread, we will add parent to currently opened tab
Before reviewing this diff, please review D1035, in which activeTab control logic is moved from ChatTabs to Provider. This diff handles only switch tab support for sidebars.

Test Plan:
Tested if switching tabs for threads works as before, tested sidebars and various scenarios:

• member thread, sidebar member
• member thread, sidebar non-member
• non-member thread, sidebar member
• non-member thread, sidebar non-member

with different

Reviewers: palys-swm, ashoat

Reviewed By: palys-swm, ashoat

Subscribers: ashoat, zrebcu411, palys-swm, Adrian, atul, subnub

Differential Revision: https://phabricator.ashoat.com/D975