undo: make adding of pictures undoable

This one is a bit hairy, because two things might happen if the
picture has a geo location:
- A dive gets a newly generated dive site set.
- The dive site of a dive is edited.
Therefore the undo command has to store keep track of that.
Oh my.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

commands/command.cpp

@@ -372,4 +372,9 @@ void removePictures(const std::vector<PictureListForDeletion> &pictures)
 	execute(new RemovePictures(pictures));
 }
 
+void addPictures(const std::vector<PictureListForAddition> &pictures)
+{
+	execute(new AddPictures(pictures));
+}
+
 } // namespace Command