WiiSave: Allow users to specify export directory

Export and ExportAll now open a directory picker (that defaults to the
previous default directory, i.e. the Dolphin user dir).

Also removes the need to return the path in the export functions since
the user knows which path they chose.

Source/Core/DolphinQt2/GameList/GameList.cpp

@@ -258,16 +258,16 @@ void GameList::OpenProperties()
 
 void GameList::ExportWiiSave()
 {
-  QMessageBox result_dialog(this);
+  const QString export_dir = QFileDialog::getExistingDirectory(
+      this, tr("Select Export Directory"), QString::fromStdString(File::GetUserPath(D_USER_IDX)),
+      QFileDialog::ShowDirsOnly);
+  if (export_dir.isEmpty())
+    return;
 
-  const QString bin_path = QString::fromStdString(WiiSave::Export(GetSelectedGame()->GetTitleID()));
-
-  result_dialog.setIcon(!bin_path.isEmpty() ? QMessageBox::Information : QMessageBox::Critical);
-  if (!bin_path.isEmpty())
-    result_dialog.setText(tr("Successfully exported save files to %1").arg(bin_path));
+  if (WiiSave::Export(GetSelectedGame()->GetTitleID(), export_dir.toStdString()))
+    QMessageBox::information(this, tr("Save Export"), tr("Successfully exported save files"));
   else
-    result_dialog.setText(tr("Failed to export save files."));
-  result_dialog.exec();
+    QMessageBox::critical(this, tr("Save Export"), tr("Failed to export save files."));
 }
 
 void GameList::OpenWiki()