Feature: Account Menu in Top Navbar

Move the account menu (→ "Me", logout, preferences, …) into an entry in the top navbar (as known from basically any other web app)

added part::frontend label

assigned to @ZugBahnHof

added type::feature label

created merge request !907 (merged) to address this issue

mentioned in merge request !907 (merged)

closed with merge request !907 (merged)

mentioned in commit d652b8f6