refs #392 XBus copy feature fine tuning

* New method: CFileUtils::copyRecursively()
* Copy the XBus directory to X-Plane plugins

src/blackgui/pluginconfigwindow.h

@@ -17,6 +17,9 @@
 
 namespace BlackGui
 {
+    /**
+     * Base class for plugin config window.
+     */
     class BLACKGUI_EXPORT CPluginConfigWindow : public QWidget
     {
         Q_OBJECT

src/blackgui/qss/stdwidget.qss

@@ -47,6 +47,14 @@ QDialog::separator:hover {
   background: transparent;
 }
 
+QFileDialog #sidebar {
+  background: black;
+}
+
+QFileDialog QToolButton {
+  background: inherit;
+}
+
 /**
   Required when dock widget is floating
   1) background-image not working on QDockWidget, so I use direct children for that