Dialog tab order implementation

- Defaults to order of definition in file
- tab-order attribtue can be set to a postive number to force towards the start, or a negative number to force towards the end

osx/dialogxml/field.h

@@ -36,6 +36,7 @@ public:
 	void handleInput(cKey key);
 	cTextField& operator=(cTextField& other) = delete;
 	cTextField(cTextField& other) = delete;
+	long tabOrder = 0;
 private:
 	bool isNumericField;
 	focus_callback_t onFocus;