Change interface: use QDateTime

- use QDateTime instead of char*-string
 - GetCostFromDuration: add end_datetime as a return value

library/include/mobilisis/calculator_functions.h

@@ -23,9 +23,10 @@ public:
 	/// <param name="tariff_cfg">Pointer to configuration</param>
 	/// <param name="vehicle_type">Type of vehicle</param>
 	/// <param name="start_datetime">Date/time of payment to be conducted in ISO8601 format (e.g. 2022-12-25T08:00:00Z) </param>
+    /// <param name="end_datetime">Date/time of park end to be conducted in ISO8601 format (e.g. 2022-12-25T08:00:00Z) </param>
 	/// <param name="durationMin">Duration of parking in minutes</param>
 	/// <returns>Returns cost (data type: double)</returns>
-	double GetCostFromDuration(Configuration* cfg, uint8_t vehicle_type, char const* start_datetime, double durationMin, bool nextDay = false, bool prepaid = false);
+    double GetCostFromDuration(Configuration* cfg, uint8_t vehicle_type, const QDateTime start_datetime, QDateTime & end_datetime, double durationMin, bool nextDay = false, bool prepaid = false);
 
     // Daily ticket
     QString GetDailyTicketDuration(Configuration* cfg, QString start_datetime, uint8_t payment_option, bool carry_over);