[web] Make NavigationPanel reusable

Summary:
The final diff of NavigationPanel refactoring. NavigationPanel receives a list of items and renders them. AppSwitcher provides a list with available apps.
Depends on D3340

Test Plan: Check if AppSwitcher still works correctly

Reviewers: benschac, atul, def-au1t, ashoat

Reviewed By: benschac, atul, ashoat

Subscribers: ashoat, Adrian, karol-bisztyga

Differential Revision: https://phabricator.ashoat.com/D3341