Allow running only one instance of application.

application/main.cpp

@@ -3,6 +3,9 @@
 #include <QDesktopWidget>
 #include <QTranslator>
 #include <QLibraryInfo>
+#include <QMessageBox>
+
+#include "application.h"
 
 #ifdef _WIN32
 #include <Windows.h>
@@ -10,7 +13,13 @@
 
 int main(int argc, char *argv[])
 {
-    QApplication a(argc, argv);
+    Application a(argc, argv);
+
+    if (!a.lock())
+    {
+        QMessageBox::warning(NULL, "Prodejna is running", "Prodejna is allready running. Only one instance can be started.");
+        return -42;
+    }
 
 #ifdef _WIN32
     QString exePath = a.applicationDirPath();