[web] Pull "statement" constants out of NotificationsModal

Summary:
Addresses feedback from @palys-swm in D4048: https://phabricator.ashoat.com/D4048#114268
Linear Issue: https://linear.app/comm/issue/ENG-1173/pull-statement-constants-out-of-notificationsmodal

Test Plan: Open NotificationsModal and ensure that things continue to look as expected.

Reviewers: def-au1t, palys-swm, benschac

Reviewed By: palys-swm

Subscribers: ashoat, Adrian, yayabosh, palys-swm

Differential Revision: https://phabricator.ashoat.com/D4109