It is inside the “user menu” only because this is where Numerus has the
same option, although it makes less sense in this case, because Numerus
is geared toward individual freelancers while Camper is for companies.
But, since it is easy to change afterward, this will do for now.
However, it should be only shown to admin users, because regular
employees have no UPDATE privilege on the company relation. Thus, the
need for a new template function to check if the user is admin.
Part of #17.
