Set window icon in the whole application instead of in BaseWindow (#3554)

This makes icon visible on Ubuntu 20.04 while using AppImage build (and possibly some other setups as well).

src/RunGui.cpp

@@ -79,6 +79,8 @@ namespace {
 
         QApplication::setStyle(QStyleFactory::create("Fusion"));
 
+        QApplication::setWindowIcon(QIcon(":/icon.ico"));
+
         installCustomPalette();
     }
 

src/widgets/BaseWindow.cpp

@@ -130,8 +130,6 @@ float BaseWindow::qtFontScale() const
 
 void BaseWindow::init()
 {
-    this->setWindowIcon(QIcon(":/images/icon.png"));
-
 #ifdef USEWINSDK
     if (this->hasCustomWindowFrame())
     {