If an expense cannot be found within a nobt the UnknownExpenseException
can be thrown

To remove an expense from a nobt a new Enpoint is provided

The VirtualBeanPropertyWriter allows us to add dynamic properties every
time Jackson serializes an instance of our Expense. Through the built-in
attribute-passing mechanism of Jackson, we pass the PropertyWriter an
instance of our LinkFactory so that the logic for actually creating the
link lives outside of the PropertyWriter and can be easily tested.

We can now also use the "delete"-link in the ApiDocumentationTest to
delete the expense.

The new config value allows to define an HTTP-header that will is used
to override the scheme of generated links, if it contains a value. This
is needed for our production environment at AWS because our application
sits behind a load-balancer that accepts all requests forwards them to
our application. The load-balancer accepts HTTPS requests but forwards
them as HTTP. Thus, generated links would be invalid if we use the
scheme of the current request to generate the link.

This prevents DeletedExpenses to render a link for deleting them.

This way, we also know when an expense was deleted.