Add icons to the buttons on the save state popup. Flip the undo buttons to match the regular buttons.

UI/UIAtlas.cpp

@@ -184,6 +184,7 @@ static const ImageMeta imageIDs[] = {
 	{"I_SHORTCUT", false},
 	{"I_KEYBOARD", false},
 	{"I_MOUSE", false},
+	{"I_FILE_SAVE", false},
 };
 
 static std::string PNGNameFromID(std::string_view id) {