Extract the system tray functionality to its own class

LibraryWindow is already a monster, so we'll try to not make it bigger.

YACReaderLibrary/trayicon_controller.h

@@ -0,0 +1,34 @@
+#ifndef TRAYICON_CONTROLLER_H
+#define TRAYICON_CONTROLLER_H
+
+#include <QtWidgets>
+#include <QSystemTrayIcon>
+
+namespace YACReader {
+
+class TrayIconController : public QObject
+{
+    Q_OBJECT
+public:
+    TrayIconController(QSettings *settings,
+                       QMainWindow *window);
+
+    void updateIconVisibility();
+
+    bool handleCloseToTrayIcon(QCloseEvent *event);
+
+    QSystemTrayIcon trayIcon;
+
+public slots:
+    void showWindow();
+
+private:
+    QSettings *settings;
+    QMainWindow *window;
+
+    QMenu *trayIconMenu;
+};
+
+}
+
+#endif // TRAYICON_CONTROLLER_H