Restructure "src/" folder

Moving files from the "src/" folder into "src/legacy", "src/macro-core",
and "src/utils" was necessary as it was becoming a bit too cluttered.

src/utils/transition-selection.hpp

@@ -0,0 +1,46 @@
+#pragma once
+#include "utility.hpp"
+
+#include <QComboBox>
+
+enum class TransitionSelectionType {
+	TRANSITION,
+	CURRENT,
+	ANY,
+};
+
+class TransitionSelection {
+public:
+	void Save(obs_data_t *obj, const char *name = "transition",
+		  const char *typeName = "transitionType");
+	void Load(obs_data_t *obj, const char *name = "transition",
+		  const char *typeName = "transitionType");
+
+	TransitionSelectionType GetType() { return _type; }
+	OBSWeakSource GetTransition();
+	std::string ToString();
+
+private:
+	OBSWeakSource _transition;
+	TransitionSelectionType _type = TransitionSelectionType::TRANSITION;
+	friend class TransitionSelectionWidget;
+};
+
+class TransitionSelectionWidget : public QComboBox {
+	Q_OBJECT
+
+public:
+	TransitionSelectionWidget(QWidget *parent, bool current = true,
+				  bool any = false);
+	void SetTransition(TransitionSelection &);
+	void Repopulate(bool current, bool any);
+signals:
+	void TransitionChanged(const TransitionSelection &);
+
+private slots:
+	void SelectionChanged(const QString &name);
+
+private:
+	bool IsCurrentTransitionSelected(const QString &name);
+	bool IsAnyTransitionSelected(const QString &name);
+};