Make it configurable to show the topmenu in sidebar

Sometimes it may be good to show the topmenu item in the sidebar …
especially if you manage multiple websites in one backend, so that you
know which website you are currently editing.
(cherry picked from commit a11819a031e4bca78d334a432e58186028a90fd0)

Conflicts:
	Resources/views/Default/sidebar.html.twig