UI: Initial Undo/Redo

Starting to develop Undo/Redo. This just implmements the undo/redo stack
and its api.

UI/undo-stack-obs.hpp

@@ -0,0 +1,46 @@
+#pragma once
+
+#include <QString>
+
+#include <deque>
+#include <functional>
+#include <string>
+#include <memory>
+
+#include "ui_OBSBasic.h"
+
+typedef std::function<void(const std::string &data)> undo_redo_cb;
+typedef std::function<void(bool is_undo)> func;
+typedef std::unique_ptr<Ui::OBSBasic> &ui_ptr;
+
+struct undo_redo_t {
+	QString name;
+	std::string undo_data;
+	std::string redo_data;
+	undo_redo_cb undo;
+	undo_redo_cb redo;
+	func d;
+};
+
+class undo_stack {
+private:
+	ui_ptr ui;
+	std::deque<undo_redo_t> undo_items;
+	std::deque<undo_redo_t> redo_items;
+	bool disabled = false;
+
+	void clear_redo();
+
+public:
+	undo_stack(ui_ptr ui);
+
+	void enable_undo_redo();
+	void disable_undo_redo();
+
+	void release();
+	void add_action(const QString &name, undo_redo_cb undo,
+			undo_redo_cb redo, std::string undo_data,
+			std::string redo_data, func d);
+	void undo();
+	void redo();
+};