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.cpp

@@ -37,6 +37,7 @@
 #include <QProcess>
 #include <QDesktopServices>
 #include <QMessageBox>
+#include <QVBoxLayout>
 
 #ifdef HAVE_QTDBUS
 #include <QDBusInterface>
@@ -46,11 +47,17 @@
 using namespace Qt::Literals::StringLiterals;
 
 MainWindow::MainWindow(QWidget *parent)
-    : FramelessWindow(parent)
+    : QWidget(parent)
     , m_am(new ActionManager)
     , m_pm(new PlaylistManager(this))
     , m_fileSystemWatcher(new QFileSystemWatcher(this))
 {
+    this->setWindowFlags(Qt::Window | Qt::WindowTitleHint | Qt::WindowSystemMenuHint | Qt::WindowMinMaxButtonsHint | Qt::WindowCloseButtonHint);
+    m_centralLayout = new QVBoxLayout(this);
+    // YYC MARK:
+    // 72 px is the height of Windows Photo Viewer's bottom line.
+    m_centralLayout->setContentsMargins(QMargins(0, 0, 0, 72)); // TODO: This value may be declared as a constant.
+
     // YYC MARK:
     // Blumis set original value is 350 x 330.
     // It is too small for modern device,
@@ -65,7 +72,7 @@ MainWindow::MainWindow(QWidget *parent)
 
     m_gv = new GraphicsView(this);
     m_gv->setScene(scene);
-    this->setCentralWidget(m_gv);
+    m_centralLayout->addWidget(m_gv);
 
     m_nav = new NavigatorView(this);
     // YYC MARK:
@@ -299,7 +306,7 @@ void MainWindow::showEvent(QShowEvent *event)
 {
     updateWidgetsPosition();
 
-    return FramelessWindow::showEvent(event);
+    return QWidget::showEvent(event);
 }
 
 void MainWindow::mouseDoubleClickEvent(QMouseEvent *event)
@@ -364,7 +371,7 @@ void MainWindow::wheelEvent(QWheelEvent *event)
         }
         event->accept();
     } else {
-        FramelessWindow::wheelEvent(event);
+        QWidget::wheelEvent(event);
     }
 }
 
@@ -372,14 +379,14 @@ void MainWindow::resizeEvent(QResizeEvent *event)
 {
     updateWidgetsPosition();
 
-    return FramelessWindow::resizeEvent(event);
+    return QWidget::resizeEvent(event);
 }
 
 void MainWindow::contextMenuEvent(QContextMenuEvent *event)
 {
     m_menu->exec(mapToGlobal(event->pos()));
 
-    return FramelessWindow::contextMenuEvent(event);
+    return QWidget::contextMenuEvent(event);
 }
 
 void MainWindow::dragEnterEvent(QDragEnterEvent *event)
@@ -390,7 +397,7 @@ void MainWindow::dragEnterEvent(QDragEnterEvent *event)
         event->ignore();
     }
 
-    return FramelessWindow::dragEnterEvent(event);
+    return QWidget::dragEnterEvent(event);
 }
 
 void MainWindow::dragMoveEvent(QDragMoveEvent *event)