[web] Introduce settings section to NavInfo

Summary:
After this change it is possible to open /settings/account path - currently empty.
Depends on D3335
Depends on D3265

Test Plan: Open /settings/account path and check if empty page is rendered (with app and community switchers and correct background).

Reviewers: benschac, atul, def-au1t

Reviewed By: atul

Subscribers: ashoat, Adrian, karol-bisztyga

Differential Revision: https://phabricator.ashoat.com/D3336