notify user their account was successfully deleted (refs #4216)

Also fixes a cornercase when admins deleted their own account. So far they would be redirected to the users list - which then refused access. Now they'll be redirected to the home landing page as well.
test helper to expect_logout.

Currently it expects both the session and the token to be cleared. This might change. But we'll always have a definition of what it means to logout we can test this way.
Merge pull request #108 from azul/feature/proper-user-deletion

notify user their account was successfully deleted (refs #4216)