Strong typedef: Use strong typedefs for date, date tick, minutes types

Add delta types
Adjust/add type conversion functions
Add various utility methods on types
Remove the various minute macros
Fix some minute conversion inconsistencies

src/vehicle_base.h

@@ -317,8 +317,8 @@ public:
 
 	/* Related to age and service time */
 	Year build_year;                    ///< Year the vehicle has been built.
-	Date age;                           ///< Age in days
-	Date max_age;                       ///< Maximum age
+	DateDelta age;                      ///< Age in days
+	DateDelta max_age;                  ///< Maximum age
 	Date date_of_last_service;          ///< Last date the vehicle had a service at a depot.
 	Date date_of_last_service_newgrf;   ///< Last date the vehicle had a service at a depot, unchanged by the date cheat to protect against unsafe NewGRF behavior.
 	uint16 reliability;                 ///< Reliability.
@@ -1536,6 +1536,6 @@ void ClearVehicleTickCaches();
 void RemoveFromOtherVehicleTickCache(const Vehicle *v);
 void UpdateAllVehiclesIsDrawn();
 
-void ShiftVehicleDates(int interval);
+void ShiftVehicleDates(DateDelta interval);
 
 #endif /* VEHICLE_BASE_H */