core: add make_manually_added_dc() function

For reasons of symmetry (there is a is_manually_added_dc()
function), create a make_manually_added_dc() function.

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

desktop-widgets/mainwindow.cpp

@@ -690,7 +690,7 @@ void MainWindow::on_actionAddDive_triggered()
 	d.dc.duration.seconds = 40 * 60;
 	d.dc.maxdepth.mm = M_OR_FT(15, 45);
 	d.dc.meandepth.mm = M_OR_FT(13, 39); // this creates a resonable looking safety stop
-	d.dc.model = strdup("manually added dive"); // don't translate! this is stored in the XML file
+	make_manually_added_dc(&d.dc);
 	fake_dc(&d.dc);
 	fixup_dive(&d);