Windows: cleaning database now shows progress window

windows/mainwindow.cpp

@@ -385,7 +385,10 @@ void MainWindow::dbRefresh() {
 }
 
 void MainWindow::dbClean() {
-    cleanDB();
+    ProgressWindow pw( mw->hInst, mw->window );
+    std::thread t( cleanDB, pw.getWindow() );
+    t.detach();
+    pw.mainLoop();
 }
 
 void MainWindow::dbManage() {