Make the burger menu independent of the Auth plugin

[Akron]

At the moment, the burger menu is specific to the Auth plugin. That is no problem at the moment, as we don't have any other non-auth depending settings. But a more general approch is favorable, where the burger menu appears, whenever there is an entry in a corresponding content_block. The settings list would then also be entries in the content block, as the login form and the logout option.