[web] Export navigation tab types

Summary:
These will be used in a couple of places
Depends on D3339
Depends on D3336

Test Plan: Just check if opening chat and calendar still works

Reviewers: benschac, atul, def-au1t

Reviewed By: benschac, atul

Subscribers: ashoat, Adrian, karol-bisztyga

Differential Revision: https://phabricator.ashoat.com/D3340