ISO: Add ISO reader code and ISO device

Adds infrastructure to read files/data from ISOs.

Also adds classes extending fs::device_base and fs::file_base in order
to allow reading files through fs namespace functions. This approach
should allow ISO data to be read by the emulator with the least changes
to existing code.

Utilities/File.h

@@ -155,7 +155,7 @@ namespace fs
 	// Virtual device
 	struct device_base
 	{
-		const std::string fs_prefix;
+		std::string fs_prefix;
 
 		device_base();
 		virtual ~device_base();