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/engine_base.h

@@ -140,7 +140,7 @@ struct Engine : EnginePool::PoolItem<&_engine_pool> {
 	uint GetPower() const;
 	uint GetDisplayWeight() const;
 	uint GetDisplayMaxTractiveEffort() const;
-	Date GetLifeLengthInDays() const;
+	DateDelta GetLifeLengthInDays() const;
 	uint16 GetRange() const;
 	StringID GetAircraftTypeText() const;