We only want to render the account link and login items in the header.
And we want only render the Multitenancy and Administrators sections in
the admin sidebar.
We include the administrators management so it's possible to give
permissions to other users to manage tenants.
In order to restrict access to other sections by typing the URL or
following a link, we're only enabling the rest of the routes when we
aren't in the multitenancy management mode.
We were displaying the total number of notifications with a message "You
have N unread notifications", but were using the total number of
notifications instead of the unread ones.
Other than simplifying the view, we can write tests using `click_link`,
which makes the tests more robust. Clicking the `.icon-notification`
element was causing some tests to fail when defining a window height of
750 pixels in the `admin_budgets` branch.
