Pass db instance to models. Pass models to QML.

src/db/sqlvehicle.h

@@ -27,7 +27,7 @@ class SqlVehicle : public QSqlTableModel
 {
     Q_OBJECT
 public:
-    explicit SqlVehicle(QObject *parent);
+    explicit SqlVehicle(QObject *parent = nullptr, QSqlDatabase db = QSqlDatabase());
     QHash<int, QByteArray> roleNames() const override;
     QVariant data(const QModelIndex &index, int role) const override;