Implement redirect functionality for pages that are not allowed to be accessed without edit permissions

As discussed in !320 (merged) we need some sort of functionality, that redirects the user to a certain location when he has not a canModify permission.

Currently, this functionality is implemented differently in some pages - some pages we even have forgotten :-/ We could provide a mixin or a middleware(?) for it, so that it is just a one-liner to implement.