Allow cloning client data stored in wxGrid attributes etc

Add wxSharedClientDataContainer class storing ref-counted client data
and use it instead of plain wxClientDataContainer in wxGridCellAttr,
wxGridCellEditor and wxGridCellRenderer classes.

This allows to keep the same client data associated with many grid cells
without having to make many copies of it.

include/wx/generic/grid.h

@@ -138,11 +138,14 @@ class wxGridDirectionOperations;
 //     class is not documented and is not public at all
 // ----------------------------------------------------------------------------
 
-class WXDLLIMPEXP_CORE wxGridCellWorker : public wxClientDataContainer, public wxRefCounter
+class WXDLLIMPEXP_CORE wxGridCellWorker : public wxSharedClientDataContainer,
+                                          public wxRefCounter
 {
 public:
     wxGridCellWorker() { }
 
+    wxGridCellWorker(const wxGridCellWorker& other);
+
     // interpret renderer parameters: arbitrary string whose interpretation is
     // left to the derived classes
     virtual void SetParameters(const wxString& params);
@@ -169,6 +172,16 @@ private:
 class WXDLLIMPEXP_CORE wxGridCellRenderer : public wxGridCellWorker
 {
 public:
+    wxGridCellRenderer()
+        : wxGridCellWorker()
+    {
+    }
+
+    wxGridCellRenderer(const wxGridCellRenderer& other)
+        : wxGridCellWorker(other)
+    {
+    }
+
     // draw the given cell on the provided DC inside the given rectangle
     // using the style specified by the attribute and the default or selected
     // state corresponding to the isSelected value.
@@ -376,7 +389,14 @@ private:
 class WXDLLIMPEXP_CORE wxGridCellEditor : public wxGridCellWorker
 {
 public:
-    wxGridCellEditor();
+    wxGridCellEditor()
+        : wxGridCellWorker(),
+          m_control(NULL),
+          m_attr(NULL)
+    {
+    }
+
+    wxGridCellEditor(const wxGridCellEditor& other);
 
     bool IsCreated() const { return m_control != NULL; }
 
@@ -524,8 +544,6 @@ protected:
     // suppress the stupid gcc warning about the class having private dtor and
     // no friends
     friend class wxGridCellEditorDummyFriend;
-
-    wxDECLARE_NO_COPY_CLASS(wxGridCellEditor);
 };
 
 // Smart pointer to wxGridCellEditor, calling DecRef() on it automatically.
@@ -535,6 +553,16 @@ typedef wxObjectDataPtr<wxGridCellEditor> wxGridCellEditorPtr;
 class wxGridCellActivatableEditor : public wxGridCellEditor
 {
 public:
+    wxGridCellActivatableEditor()
+        : wxGridCellEditor()
+    {
+    }
+
+    wxGridCellActivatableEditor(const wxGridCellActivatableEditor& other)
+        : wxGridCellEditor(other)
+    {
+    }
+
     // In this class these methods must be overridden.
     virtual wxGridActivationResult
     TryActivate(int row, int col, wxGrid* grid,
@@ -705,7 +733,8 @@ private:
 // class may be returned by wxGridTable::GetAttr().
 // ----------------------------------------------------------------------------
 
-class WXDLLIMPEXP_CORE wxGridCellAttr : public wxClientDataContainer, public wxRefCounter
+class WXDLLIMPEXP_CORE wxGridCellAttr : public wxSharedClientDataContainer,
+                                        public wxRefCounter
 {
 public:
     enum wxAttrKind