[web] Open chat when user clicks inbox icon

Summary: Navigate a user to a chat when the icon is clicked.

Test Plan: Use this button in a couple of places and verify that the user was navigated to the chat.

Reviewers: def-au1t, atul, benschac

Reviewed By: atul

Subscribers: ashoat, Adrian, yayabosh

Differential Revision: https://phabricator.ashoat.com/D4144