[web] Introduce AddMembersList component

Summary:
Introduce component grouping users and rendering list based on search results in AddMembersModal.
I used common logic with native app, where only users from parent thread have "notice" set to "undefined". It's the reason, why after grouping the title: "Users in parent thread" is added manually.

Test Plan: The list can be tested after introducing AddMembersModal

Reviewers: palys-swm, benschac, atul, ashoat

Reviewed By: palys-swm, ashoat

Subscribers: ashoat, palys-swm, Adrian, atul, karol-bisztyga, benschac, yayabosh

Differential Revision: https://phabricator.ashoat.com/D3741