ui: subwindow when resize mainwindow

* disable drop in qtlineedit
    fixes bug where when file is dropped in the lineedit with text,
    the the file will be added as text midst the existing text
* move message to start from script before layout loading so it will load right
(only when started without script on linux)
* center subwindow when mainwindow size changes

src/lib_gui/qt/window/QtWindowStack.h

@@ -31,7 +31,10 @@ public:
 
 	QtWindowStackElement* getTopWindow();
 	QtWindowStackElement* getBottomWindow();
-	size_t getWindowCount();
+
+    size_t getWindowCount();
+
+    void centerSubWindows();
 
 public slots:
 	void pushWindow(QtWindowStackElement* window);