[web] Introduce ThreadMember component

Summary:
Introducing component rendering single thread member on the list in thread modal.
It contains menu with actions (added in the next diffs) and displays user role as a label. When the menu is open, the style is a bit different, so it keeps the menu state and receives onMenuChange prop, as the parent component also needs to know the menu status (to disable scrolling when it's open)

Test Plan: Component can be tested after introducing thread members modal.

Reviewers: palys-swm, benschac, atul

Reviewed By: palys-swm

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

Differential Revision: https://phabricator.ashoat.com/D3379