user's logged in state is not always synchronized across tabs

[shane-tomlinson]

This was brought up by @ncalexan.

Scenario 1:

1. User is unauthenticated, has two tabs (Tab A, and Tab B) open, both to the signin or signup page.
2. In Tab A , the user signs in and is shown the settings page.
3. Nothing happens in Tab B.

Expected

1. Tab B redirects to the settings page.

Scenario 2:

1. User is authenticated, has two tabs (Tab A, and Tab B) open to the /settings page.
2. In Tab A, the user signs out and is sent to the /signin page.
3. Tab B does nothing until the user attempts to do something.

Expected

1. Tab B redirects to the /signin page.

We currently synchronize session state on email verification, but not otherwise.