[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:
With:
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