[web] Introduce Apps page

Summary:
Introduce Apps panel similar to existing in native app.
FontAwesome icons will soon be replaced by SWMIcons in follow-up diff.

Test Plan: Run web and confirm that switching calendar on and off works

Reviewers: palys-swm, benschac, atul

Reviewed By: palys-swm, benschac

Subscribers: ashoat, Adrian, atul, karol-bisztyga

Differential Revision: https://phabricator.ashoat.com/D3266