private void PartnersClick(object sender, RoutedEventArgs e)
        {
            string content;

            if (sender is Button)
            {
                Button button = (Button)sender;
                content = button.Content.ToString();
            }
            else
            {
                MenuItem menu = (MenuItem)sender;
                content = menu.Header.ToString();
            }

            if (content == "Partnerek")
            {
                PartnersVM     partnersVM = new PartnersVM();
                PartnersWindow partners   = new PartnersWindow {
                    DataContext = partnersVM, Title = content
                };
                partners.Show();
            }
            else
            {
                ContactsVM     contacts = new ContactsVM();
                PartnersWindow partners = new PartnersWindow {
                    DataContext = contacts, Title = content
                };
                contacts.LoadPartnersList();
                partners.Show();
            }
        }
        private void ContactAddClick(object sender, RoutedEventArgs e)
        {
            ContactsVM contacts = new ContactsVM {
                IsPartnerAdd = ((PartnerFormVM)DataContext).ChosenPartner.ID, PartnerContactList = ((PartnerFormVM)DataContext).ContactsList
            };
            PartnersWindow partners = new PartnersWindow {
                DataContext = contacts, Title = "Elérhetőségek"
            };

            contacts.LoadPartnersList();
            partners.ShowDialog();
        }