[web] Introduce ThreadMenu

Summary:
Introduce top bar thread menu. Currently, without any actions.
Menu disappears after clicking outside.

The eslint-ignore is only for current diff, as the following will add actions that use ThreadInfo.

Test Plan: Tested the menu with actions (in following diffs) in many different thread types, to make sure proper items are displayed for each thread.

Reviewers: palys-swm, benschac, atul, ashoat

Reviewed By: palys-swm, benschac, ashoat

Subscribers: ashoat, Adrian, atul, karol-bisztyga

Differential Revision: https://phabricator.ashoat.com/D3187