Improve the warning shown to the user when closing the application wile
in the planner. We now allow the user to directly discard the planned
dive, save it into the dive log, or cancel the operation altogether.
If they save into the dive log, or if they modified the dive log before
starting the planner, a second warning about the unsaved dive log
changes will be shown.
Signed-off-by: Michael Keller <mikeller@042.ch>
