LibGUI: Add horizontal scrollbar to GTableView.

Now we can scroll content in both directions if it won't fit in the view.

Applications/ProcessManager/main.cpp

@@ -16,6 +16,7 @@ int main(int argc, char** argv)
     GApplication app(argc, argv);
 
     auto* widget = new GWidget;
+    widget->set_fill_with_background_color(false);
     widget->set_layout(make<GBoxLayout>(Orientation::Vertical));
 
     auto* toolbar = new GToolBar(widget);