This way we follow the convention of one stylesheet per component.
Note that we depend on Foundation's `menu` class for some of the
styles and JavaScript behavior, so we're keeping both the `menu` and
`account-menu` classes.
We're trying to be consistent; in the past, we had the partials
"shared/admin_login_items", "layouts/notification_item" and
"devise/menu/login_items". Now we're moving all these partials to
components in the `Layout` namespace.
This way we remove the duplication in the layouts which had these links.
Since we're now passing the `current_user` option to partials in all
cases, IMHO the code is easier to follow if we use the
`Layout::NotificationItemComponent` instead of its partial.
