refactor: remove frameless window

remove frameless window and merge it into mainwindow. because we do not need frameless and transparent window, so most of its functions are removed in previous commits.

app/mainwindow.h

@@ -5,14 +5,13 @@
 #ifndef MAINWINDOW_H
 #define MAINWINDOW_H
 
-#include "framelesswindow.h"
-
 #include <QParallelAnimationGroup>
 #include <QPropertyAnimation>
 #include <QPushButton>
 
 QT_BEGIN_NAMESPACE
 class QMenu;
+class QVBoxLayout;
 class QGraphicsView;
 class QFileSystemWatcher;
 QT_END_NAMESPACE
@@ -22,7 +21,7 @@ class PlaylistManager;
 class GraphicsView;
 class NavigatorView;
 class BottomButtonGroup;
-class MainWindow : public FramelessWindow
+class MainWindow : public QWidget
 {
     Q_OBJECT
 
@@ -104,6 +103,7 @@ private:
     NavigatorView *m_nav;
 
     QMenu *m_menu;
+    QVBoxLayout * m_centralLayout = nullptr;
     QFileSystemWatcher *m_fileSystemWatcher;
     BottomButtonGroup *m_bottomButtonGroup;
 };