ui: Show title bar at top and scroll bar at bottom in code view snippet list if necessary (issues #432, #479)

* Show title bar at top of snippet list if first file is cut off
* Show scrollbar at bottom of snippet list if last snippet if cut off and horizontally scrollable
* Extended scrollRequest API to different ScrollTarget modes
* Fixed snippet extension broken if maximized first
* Split off title bar functionality to separate class QtCodeFileTitleBar

src/lib_gui/qt/element/QtCodeFileTitleBar.h

@@ -0,0 +1,53 @@
+#ifndef QT_CODE_FILE_TITLE_BAR_H
+#define QT_CODE_FILE_TITLE_BAR_H
+
+#include "qt/element/QtCodeFileTitleButton.h"
+#include "qt/element/QtIconButton.h"
+
+class QLabel;
+class QtCodeFileTitleButton;
+class QtIconStateButton;
+
+class QtCodeFileTitleBar
+	: public QtHoverButton
+{
+	Q_OBJECT
+
+signals:
+	void minimize();
+	void snippet();
+	void maximize();
+
+public:
+	QtCodeFileTitleBar(QWidget* parent = nullptr, bool isHovering = false);
+
+	QtCodeFileTitleButton* getTitleButton() const;
+
+	void setRefString(const QString& refString);
+
+	void setMinimized(bool hasSnippets);
+	void setSnippets();
+	void setMaximized(bool hasSnippets);
+
+	void updateFromOther(const QtCodeFileTitleBar* other);
+
+private slots:
+	void clickedTitleBar();
+
+	void enteredTitleBar(QPushButton* button);
+	void leftTitleBar(QPushButton* button);
+
+	void clickedMinimizeButton();
+	void clickedSnippetButton();
+	void clickedMaximizeButton();
+
+private:
+	QtCodeFileTitleButton* m_titleButton;
+	QLabel* m_referenceCount;
+
+	QtIconStateButton* m_minimizeButton;
+	QtIconStateButton* m_snippetButton;
+	QtIconStateButton* m_maximizeButton;
+};
+
+#endif // QT_CODE_FILE_TITLE_BAR_H