Fix wxGTK wxDataViewRenderers' alignment handling

Don't apply alignment to native controls in SetAlignment() method, where
it may not be known yet due to column-to-renderer inheritance if
wxDVR_DEFAULT_ALIGNMENT is used (the default). Move such code to
GtkUpdateAlignment() (which was made virtual) in all renderers.

This fixes unintended right-aligning of columns with GTK+ 2 when default
alignment was used.

include/wx/gtk/dvrenderer.h

@@ -53,7 +53,7 @@ public:
 
     GtkCellRenderer* GetGtkHandle() { return m_renderer; }
     void GtkInitHandlers();
-    void GtkUpdateAlignment() { GtkApplyAlignment(m_renderer); }
+    virtual void GtkUpdateAlignment() { GtkApplyAlignment(m_renderer); }
 
     // return the text renderer used by this renderer for setting text cell
     // specific attributes: can return NULL if this renderer doesn't render any