R1:0fa411083f72

Show an "approval queue" item on the home page for admins, and sort out menu item visibility

Summary:
- If you're an administrator and there are users waiting for approval, show a count on the home page.
- Sort out the `isUserActivated()` access check.
- Hide all the menu widgets except "Logout" for disabled and unapproved users.
- Add a "Log In" item.
- Add a bunch of unit tests.

Test Plan: Ran unit tests, clicked around as unapproved/approved/logged-in/logged-out users.

Reviewers: btrahan…