-- New hidden Parameter: RequireAbsenceTypeInUrlP
    By setting RequireAbsenceTypeInUrlP to '1' an 'Absence Type' can be set only by passing
    the respective absence_type_id as an URL parameter.
    User is provided only with links for Absence Types she's allowed to create. She won't be able
    to edit the type anymore through the absence select box that is otherwise shown on this page.
    A callback can be set up to prevent that users create unauthorized absences by URL manipulation.
    For now provisional solution, RequireAbsenceTypeInUrlP is therfore a hidden parameter