[web] Introduce close button in Label component

Summary:
Introduce close action for Label component. The aim is to use in MembersModal in the list of pending users to add to the thread.

Without close action:

Test Plan: Currently used Labels don't change because introduced property is optional and will be used in the next diff.

Reviewers: palys-swm, benschac, atul

Reviewed By: palys-swm

Subscribers: ashoat, Adrian, atul, karol-bisztyga, yayabosh

Differential Revision: https://phabricator.ashoat.com/D3875