chore: allow dragging window from titlebar when maximized (#178)

This better matches titlebar behavior of Windows and KDE, and probably a lot more other environments, it also allows for easier unmaximizing because the current titlebar has no dedicated maximize/restore button.

Note: This is somewhat problematic on Windows, thus we only apply the change to other platforms for now.

app/titlebar.cpp

@@ -129,8 +129,14 @@ void TitleBar::mouseMoveEvent(QMouseEvent *event)
         }
     }
 
+    bool optionalMaximized = false;
+    #if defined(Q_OS_WIN)
+        optionalMaximized = isMaximized();
+    #endif
+
     if (event->buttons() & Qt::LeftButton && m_dragPending
-        && !window()->isMaximized() && !window()->isFullScreen()) {
+        && !window()->isFullScreen() && !optionalMaximized) {
+        
         if (QWindow *wh = window()->windowHandle()) {
             if (!wh->startSystemMove())
                 window()->move(event->globalPosition().toPoint() - m_moveStartPos);