Add wxListCtrl::SetHeaderAttr()

This method can be used to change the list view header appearance.

Add the method declaration, documentation, show it in the sample and implement
it for wxMSW (only, for now).

include/wx/msw/listctrl.h

@@ -16,6 +16,7 @@
 #include "wx/vector.h"
 
 class wxMSWListItemData;
+class wxMSWListHeaderCustomDraw;
 
 // define this symbol to indicate the availability of SetColumnsOrder() and
 // related functions
@@ -115,6 +116,9 @@ public:
     bool SetForegroundColour(const wxColour& col);
     bool SetBackgroundColour(const wxColour& col);
 
+    // Header attributes
+    virtual bool SetHeaderAttr(const wxItemAttr& attr) wxOVERRIDE;
+
     // Gets information about this column
     bool GetColumn(int col, wxListItem& item) const;
 
@@ -461,6 +465,10 @@ private:
     void OnCharHook(wxKeyEvent& event);
 
 
+    // Object using for header custom drawing if necessary, may be NULL.
+    wxMSWListHeaderCustomDraw* m_headerCustomDraw;
+
+
     wxDECLARE_DYNAMIC_CLASS(wxListCtrl);
     wxDECLARE_EVENT_TABLE();
     wxDECLARE_NO_COPY_CLASS(wxListCtrl);