Eliminate use of __attribute__

Ideally this would be standard C++, but here I've settled for things that should be supported by both clang and VS/cl.exe:
- Deprecated attribute retained, but now uses __declspec syntax
- Packed attribute replaced with pragma pack, except one instance where it unnecessary
- Aligned attribute replaced with explicit padding bytes inserted in the structs where needed
- Unused attribute simply removed (though where possible, the unused entities were also removed)

osx/classes/scenario.h

@@ -100,7 +100,7 @@ public:
 	cOutdoors* outdoors;
 	cTown* towns;
 	
-	char(& scen_strs(short i))[256] __attribute__((deprecated));
+	__declspec(deprecated) char(& scen_strs(short i))[256];
 	cScenario& operator = (legacy::scenario_data_type& old);
 	void append(legacy::scen_item_data_type& old);
 	void writeTo(std::ostream& file);