This model is only needed when in plan mode. To enable multiple
profilewidgets at the same time (e.g. for the mobile app or
for printing), make the pointer to DivePlannerPointsModel a
member variable that is initialized at construction time.
Moreover, allow passing null as the DivePlannerPointsModel,
in which case planning will be disabled. This will be useful
for simple printing.
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>