This one is tricky, as when browsing through the types-combobox,
the user is presented with presets without actually changing the
dive. We do not want an undo-command for every change-event in
the combo-box.
Therefore, implement a scheme analoguous to the weight-editing:
A temporary row can be set / committed or reset. Sadly, the
code is more complex because we have to consider the planner,
which is not included in the undo system.
Firstly, the planner uses a different model, therefore all
interactions are channeled through setData() with special roles.
Secondly, in the planner we shouldn't place an undo command,
but simply overwrite the dive.
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>