Added support for saving receipts.

core/service.h

@@ -67,7 +67,7 @@ public:
         return ret;
     }
 
-    void save(QSharedPointer<T> entity) {
+    virtual void save(QSharedPointer<T> entity) {
         if (!checkPermission(PERM_ADD)) {
             return;
         }
@@ -93,7 +93,7 @@ public:
         emit dataChanged();
     }
 
-    void update(QSharedPointer<T> entity) {
+    virtual void update(QSharedPointer<T> entity) {
         if (!checkPermission(PERM_EDIT)) {
             return;
         }