unify i/o error reporting in the model

- use Utils::FileSaver
- as a side effect, don't rewrite the desktop file with the same content
  if it already exists
- pop up message boxes on errors - this is likely to be more visible
  than qWarning()s/nothing
  - this is implemented in a somewhat strange way with the model itself
    doing the gui interaction, but that seems to be the simplest
    solution given the qt class design

src/plugins/qt4projectmanager/qt-maemo/maemodeployconfigurationwidget.cpp

@@ -120,11 +120,7 @@ void MaemoDeployConfigurationWidget::addDesktopFile()
         return;
     MaemoDeployableListModel *const model
         = m_deployConfig->deployables()->modelAt(modelRow);
-    QString error;
-    if (!model->addDesktopFile(error)) {
-        QMessageBox::warning(this, tr("Could not create desktop file"),
-             tr("Error creating desktop file: %1").arg(error));
-    }
+    model->addDesktopFile();
     ui->addDesktopFileButton->setEnabled(model->canAddDesktopFile());
     ui->tableView->resizeRowsToContents();
 }
@@ -161,11 +157,7 @@ void MaemoDeployConfigurationWidget::addIcon()
         return;
     }
 
-    QString error;
-    if (!model->addIcon(newFileName, error)) {
-        QMessageBox::critical(this, tr("Could Not Add Icon"),
-             tr("Error adding icon: %1").arg(error));
-    }
+    model->addIcon(newFileName);
     ui->addIconButton->setEnabled(model->canAddIcon());
     ui->tableView->resizeRowsToContents();
 }