We weren't using the `admin-top-bar` class since commit e6c1cf774, and
we can always use the `.admin .top-bar` selector if we need to. And the
`row expanded` classes basically give an element a width of 100%, which
is already the default width for block elements.
We were using the same code for the button in both the public and admin
headers, so we're removing the duplication.
Since the menu and the button must go together, and the contents of the
menu are different for different layouts, we're passing these contents
using a block.
Note the ID of the menu was `responsive-menu` in the public section but
`responsive_menu` in the admin section. Since we usually use underscores
for IDs and dashes for classes, we're keeping the one with the
underscore.
So now it uses the same interface and styles as the main layout. On
small screens, it's easier to play with the menu when the button is on
the left because the menu it opens is aligned to the left.
Note that now we can get rid of the title-bar class; we didn't use the
styles in the public area since commit dcec003d0, and we were overriding
all the Foundation styles in the admin area with the exception of the
padding, which we no longer need.
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.
This way it's easier to refactor it.
Note we're using `with_request_url` in the tests because the component
renders the locale switcher, which needs a URL in order to work. This
doesn't affect whether we're in the management section or not.
