[web] Introduce member action menu items in ThreadMember component

Summary:
Introduce thread member actions - to remove member or promote him to an admin. The conditions are the same as in native app.

Test Plan: Can be tested after introducing members modal.

Reviewers: palys-swm, benschac, atul, ashoat

Reviewed By: palys-swm, benschac, ashoat

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

Differential Revision: https://phabricator.ashoat.com/D3380